Sure, the brokers bear some responsibility, but they don’t make their clients’ decisions for them. For most people it’s very easy to figure, “Hey, I’ll probably be moving in five years anyway, I might as well save on payments now.” Or maybe they just take a gamble hoping to win out over a fixed rate. That in two years they’ll have a better debt-to-income ratio and a better credit score. Etc.

And in terms of doing things right the first time around, a mortgage broker’s responsibility is to secure a loan for their client that the client agrees to. Like a lot of other things dealing with money, the most attractive option isn’t usually the best one. (Though I would be remiss if I didn’t point out that for a lot of people, an ARM does exactly what they want.)