Answer: Both. For many people, it was rational to participate in the mortgage bubble even if they thought it might (would) end in tears. On the other hand, even smart people can be taken in by bubble logic if everyone around them is convinced. For example, here is a 2006 discussion from Brad DeLong's blog of a column by Paul Krugman, making the case that most of the country was not experiencing a bubble, and that zoning was the main culprit for coastal price increases (hence prices were sustainable). If you were a CDO modeler in 2006 and believed that argument, you might not have even considered that your model assumptions were way too optimistic -- even with people like Robert Shiller (and me) shouting that we were in the midst of a gigantic bubble.
Some of the best journalistic coverage I have found of the mortgage bubble is from Ira Glass and This American Life (audio, pdf transcript). They get the "local color" right from top to bottom: self-interested individual borrowers, local mortgage brokers rushing to assemble as many loans as possible, to be sold to Wall Street banks and repackaged as CDOs, rated by agencies like Moody's and S&P that were making record profits from fees, and sold to investors chasing yield in the midst of a liquidity glut caused by low interest rates. From their coverage you can see the incentives were messed up from top to bottom, and that many individuals anticipated trouble ahead, but couldn't put up a fight without risking their careers or bonuses. Some excerpts below.
borrower: ...I wouldn't have loaned me the money. And nobody that I know would have loaned me the money. I know guys who are criminals who wouldn't loan me that and they break your knee-caps. I don’t know why the bank did it. ...Nobody came and told me a lie: just close your eyes and the problem will go away. That's wasn’t the situation. I needed the money. I'm not trying to absolve myself of anything. I thought I could do this and get out of it within 6 to 9 months. The 6 to 9 month plan didn’t work so I’m stuck.
mortgage broker ...it was unbelievable. We almost couldn’t produce enough to keep the appetite of the investors happy. More people wanted bonds than we could actually produce. That was our difficult task, was trying to produce enough. They would call and ask “Do you have any more fixed rate? What have you got? What’s coming?” From our standpoint it's like, there's a guy out there with a lot of money. We gotta find a way to be his sole provider of bonds to fill his appetite. And his appetite’s massive.
...my boss was in the business for 25 years. He hated those loans. He hated them and used to rant and say, “It makes me sick to my stomach the kind of loans that we do.” He fought the owners and sales force tooth and neck about these guidelines. He got same answer. Nope, other people are offering it. We're going to offer them too. We’re going to get more market share this way. House prices are booming, everything’s gonna be good. And ... the company was just rolling in the cash. The owners and the production staff were just raking it in.
Wall St. banker ...No income no asset loans. That's a liar's loan. We are telling you to lie to us. We're hoping you don't lie. Tell us what you make, tell us what you have in the bank, but we won't verify? We’re setting you up to lie. Something about that feels very wrong. It felt wrong way back when and I wish we had never done it. Unfortunately, what happened ... we did it because everyone else was doing it.
...All the data that we had to review, to look at, on loans in production that were years old, was positive. They performed very well. All those factors, when you look at the pieces and parts. A 90% NINA loan from 3 years ago is performing amazingly well. Has a little bit of risk. Instead of defaulting 1.5% of the time it defaults at 3.5% of the time. That’s not so bad. If I’m an investor buying that, if I get a little bit of return, I’m fine.
CDO packager: ... In 2005, we had an internal debate here because there were two banks coming to us, why don’t you do a deal with us, BBB securities, you get paid a million bucks in management fees per year. Very clear, just like that, in 2005. And we declined those deals. We just don't believe those BBB RMBS assets are money-good. And we thought if we do a CDO of those, that's gonna blow up completely. We were early in '05 by not wanting to do those deals. People were laughing at us. Saying you're crazy. You’re hurting your business. Why don’t you want to make ... Per deal, you could make a million dollars a year.