This argument is obviously foolish. There is nothing comparable between interest and trade. There is equity in business transactions because there is a mutual agreement between the two parties and both stand to gain or lose. In trading, a seller sells an article to the buyer at a price mutually acceptable to both, and the matter ends there.
But taking interest is a clearcut case of exploitation. A person with surplus money, which he does not need, lends it to someone who is in dire need. The needy person agrees to pay interest which he can ill afford; not because it is acceptable to him but because of his compelling situation.