While I think Baha'u'llah is indirectly praising those who loan on "benevolent terms" in the following passage, and forbids usury, He does permit interest.
As to thy question concerning interest and profit on gold and silver: Some years ago the following passage was revealed from the heaven of the All-Merciful in honour of the one who beareth the name of God, entitled Zaynu'l-Muqarrabín+F1 --upon him be the glory of the Most Glorious. He--exalted be His Word--saith: Many people stand in need of this. Because if there were no prospect for gaining interest, the affairs of men would suffer collapse or dislocation. One can seldom find a person who would manifest such consideration towards his fellow-man, his countryman or towards his own brother and would show such tender solicitude for him as to be well-disposed to grant him a loan on benevolent terms.+F2 Therefore as a token of favour towards men We have prescribed that interest on money should be treated like other business transactions that are current amongst men. Thus, now that this lucid commandment hath descended from the heaven of the Will of God, it is lawful and proper to charge interest on money, that the people of the world may, in a spirit of amity and fellowship and with joy and gladness, devotedly engage themselves in magnifying the Name of Him Who is the Well-Beloved of all mankind. Verily He ordaineth according to His Own choosing. He hath now made interest on money lawful, even as He had made it unlawful in the past. Within His grasp He holdeth the kingdom of authority. He doeth and ordaineth. He is in truth the Ordainer, the All-Knowing.
Render thou thanks unto thy Lord, O Zaynu'l-Muqarrabín, for this manifest bounty.
Many ecclesiastics in Persia have, through innumerable designs and devices, been feeding on illicit gains obtained by usury. They have contrived ways to give its outward form a fair semblance of lawfulness. They make a plaything of the laws and ordinances of God, but they understand not.
However, this is a matter that should be practised with moderation and fairness. Our Pen of Glory hath, as a token of wisdom and for the convenience of the people, desisted from laying down its limit. Nevertheless We exhort the loved ones of God to observe justice and fairness, and to do that which would prompt the friends of God to evince tender mercy and compassion towards each other. He is in truth the Counsellor, the Compassionate, the All-Bountiful. God grant that all men may be graciously aided to observe that which the Tongue of the One true God hath uttered. And if they put into practice what We have set forth, God--exalted be His glory--will assuredly double their portion through the heaven of His bounty. Verily He is the Generous, the Forgiving, the Compassionate. Praise be unto God, the Most Exalted, the Most Great.
Nevertheless the conduct of these affairs hath been entrusted to the men of the House of Justice that they may enforce them according to the exigencies of the time and the dictates of wisdom.
Once again We exhort all believers to observe justice and fairness and to show forth love and contentment. They are indeed the people of Bahá, the companions of the Crimson Ark. Upon them be the peace of God, the Lord of all Names, the Creator of the heavens.
+F1 One of the early believers who is best known to the friends for his reliable transcriptions of the Tablets of Bahá'u'lláh. (See Memorials of the Faithful pp. 150-153.)
+F2 Such loans as bear no interest and are repayable whenever the borrower pleases.
(Tablets of Baha'u'llah, pp. 132
While we believe the spiritual and moral truths of "Islam" are eternal, as is the proof of the Qur'an, we do not believe that the Dispensation of Muhammad was to last forever (in part due to the competence of His followers, Shoghi Effendi wrote in a letter on his behalf).
"In the Bayan the Bab says that every religion of the past was fit to become universal. The only reason why they failed to attain that mark was the incompetence of their followers. He then proceeds to give a definite promise that this would not be the fate of the Revelation of 'Him Whom God would make manifest', that it will become universal and include all the people of the world. This shows that we will ultimately succeed. But could we not through our shortcomings, failures to sacrifice, and reluctance to concentrate our efforts in spreading the Cause, retard the realization of that ideal. And what would that mean? It shall mean that we will be held responsible before God, that the race will remain longer in its state of waywardness, that wars would not be so soon averted, that human suffering will last longer."
(From a letter written on behalf of Shoghi Effendi to the National Spiritual Assembly of the United States and Canada, February 20, 1932: Living the Life, pp. 3-4)
But this failure for previous Faiths to become universal also rests to some degree on God not having provided, before the Baha'i Dispensation, a clear and unbreakable Successorship, for whatever mysterious reasons:
"...There is certainly an element of truth at the basis of the organization of the Christian Church. For instance, the primacy of Peter and his right to succession after Jesus have been established by the latter, though only orally and not in an explicit and definite language. The real reason why Christ did not make some explicit statement regarding His succession is not known, and cannot be known. For how can we, poor humans, claim to unravel the mysteries of God's mind and purpose, and to grasp the inscrutable dispensations of His providence. The utmost we can do is to give some explanations, but these must necessarily fail to give the fundamental reason to the problem we seek to solve."
(From a letter written on behalf of Shoghi Effendi to an individual believer, December 28, 1936)
As the Kitab-i-Iqan states, God does test man as well as man being responsible for his own actions.
And even the Baha'i Faith is to have its own laws renewed in a thousand or thousands of years. But every Manifestation of God has the right to abrogate the laws of the prior dispensation(s).
As far as a comparison of loaning to slavery, while usury (high interest loans) sure can be like slavery, and is a despicable practice, loans have brought many people out of poverty, especially in the context of social programs like micro-finance: http://www.onecountry.org/oc83/oc8302as.html
. People all over the world pay for mortgages on their homes, so they can enjoy their homes in the present, even as they gradually become owners. Some countries allow interest but put a cap on the amount of interest. People do not feel they are being cheated by taking such loans (unless the loans are deceptive about the terms, as happened especially strongly in the U.S. recently).
An admittedly challenging situation is for those who are given "high-risk" loans. These people have proven in the past that they are not as likely to repay a loan (or they meet certain conditions that put them statistically in such a position). But for a company to make money, they have to be able to cover their costs, and they may lose money if such people fail to return their investment. So they charge higher rates to such people. The government may have some means of bailing people out who get into a trap where they can't pay off their debts, but this can still be a big burden for many people who are already poor. Yet still many are grateful to have a chance to get some kind of loan to get what they need to get a business going, etc., and sometimes people who default did squander their opportunity (maybe this is one reason why the Baha'i micro-credit efforts offer some moral and planning training). Still, it does raise moral questions.
But normally, a low-interest loan is little different from any other service you pay others for. You can pay people to have immediate access to cash which you can invest in your own business, etc. If you gamble or waste the money away, you can't really blame the lender. If someone sells me some roasted meat on the street (to take your earlier example), one might say that he is enabling me and encouraging me to get fat. I could claim that I can't help avoiding the delicious meat, and I am becoming his slave because he cooks it so well, and that other people will fall into the same trap, etc., so they should avoid buying anything from anyone, but we all realize that this is not reasonable. The important thing is the degree. Of course, that doesn't mean certain extremely frequently addictive things like gambling, drugs, etc., should not be prohibited. But loans are different from gambling because gambling gives a mostly false sense of hope that one can earn more (and also serves no benefit to society in the process), whereas a loan can be used for many good things, just as meat (or other food) can be used to bring me a health when taken in moderation....