And if the loan shark weren’t there providing his service, his clients would be strictly worse off. He’s not forcing them to borrow money—he’s offering, and they’re free to say no.
Sorry, this is not an argument. There are things that can be illegal and/or immoral (loan sharking is both), even though there are "no better options". This is not how to build a sustainable society, and is one of the issues causing so many problem in today's society.
And if the loan shark weren’t there providing his service, his clients would be strictly worse off. He’s not forcing them to borrow money—he’s offering, and they’re free to say no.