Let me preface this by saying that the current financial mess, like any problem big enough to be worth talking about, is complicated; there isn't just one thing that caused it or one thing we can change to fix it. There are as many suggestions for what caused the mess as there are people talking about it, and every cause I've seen suggested probably contributed a little to the mess.
For the most part, we're missing the point if we think we should just blame the top executives. For the most part, those executives didn't start out as what we'd think of as solidly ethical, get to positions of power, and then suddenly become slime. They all started their careers years ago in a system that rewarded short-term thinking and didn't care about long term stupidity, and a lot of other people started their careers at the same time. The reason the ones at the top now got there is not that they were more evil, it's that they were better at playing the game as it exists. The more clever they were at coming up with bizarre schemes that would make them a bunch of money today and leave someone else holding the bag tomorrow, the better. The ones who would stop and say "hey, wait a minute, this isn't sustainable, we should do something sane" made less profits in the short term, and had to go get jobs as shoe salesmen.
To pick specifically on the dodgy mortgage brokers some others were picking on above: if you were working as a front-line broker for a sub prime company 5 years ago, and you made sure that the people that came to you wanting loans really understood that their payments were going to go up a whole lot after two years and convinced them not to buy that house if they wouldn't be able to afford it, and the guy in the next cube over just glossed over all those boring numbers with a smile, when performance review time came around, you got to start flipping burgers and the other guy got a bonus. Yeah, you probably are more ethical than the other guy, but if we blame him, and not the business climate that rewarded him and punished you, we won't be any closer to avoiding having the same thing again.
And as for what created the system where all we care about is short term paper profits, we don't just get to blame a few Wall Street execs. All of us who put our savings in diversified mutual funds and never did anything more than look at the account balance on our quarterly statement and smile bear some of the blame.
If you want to fix it long term, make it harder to do well in the long term by investing in companies that are screwing the future for profits today. Take the tax incentives away from parasitic paper shuffling like derivatives and short selling, and instead favor buying actual shares and holding them for years. Find a tweak to the system that makes it more attractive to invest in a small number of companies and then pay attention to what they're doing, rather than just diversifying over such a wide swath that you don't care if one company fucks up as long as the market rises.
But mainly, try to suss out what's wrong with the system and how to make it better, rather than looking for individuals to blame.