1) They thought the pollsters were wrong and the plan either wasn’t unpopular or wouldn’t be unpopular once they explained it.
2) They were less worried — at least at that moment — about what would be unpopular with the electorate and more worried about what would be unpopular with the base.
3) They really believed in the Ryan budget, and were willing to lose seats, and perhaps even the majority, over it.
4) They believed that the details would matters less than their conviction. That is to say, being seen as “making hard choices” would be more popular than the choices themselves would be unpopular.
5) It fit the individual needs of key actors at a particular moment in time: Boehner needed to support something bold and conservative, Cantor needed to be pushing something more conservative than Boehner seemed comfortable with, Tea Party politicians needed to show they weren’t getting sucked into Washington dealmaking, Ryan needed to make good on his promises to take on entitlements, etc.
All good ideas, I think, though I think the true mixture of motives involves some of these more than others. I think the first part of 3 is true, for instance, but I do not believe the Republicans think it will cost seats. In fact, I'm starting to think a combination of 1 and the first part of 3 may be the key.
The worldview of the Republican party, and in particular the psychology of Republican politicians, is something very foreign to me, but I think I'm starting to get some aspects of it. I'm coming to the conclusion that class affects the Republican worldview much more than I've thought before, and may in fact be the primary hermeneutic by which Republicans create their ideology and take stances.
I got to this point by starting from the principle that people are motivated primarily by self-interest and emotion. For all our arguments and complicated rationales, the vast majority of the time people choose their political stances according to fear, resentment, anger, compassion, and loyalty. And almost nobody is aware of this fact.
Our emotional investment in politics, usually grounded primarily in self-interest, combines then with our natural, well-established psychological tendency to take special notice of things that corroborate our views and not notice things that don't. Add in people's natural desire to avoid conflict and thus associate most often with people who agree with them, and we can see how all this leads inevitably to the acceptance of false or inconsistent ideas as absolutely true. Now let's throw in a media that views politics as sport, and that intentionally avoids any attempt to address the substance of complicated political issues for fear of taking one side (more specifically, of being forced to admit that the left is right on any subject).
Now throw in the particular plight of Republicans politicians, who are rich and white almost to a man, and overwhelmingly male. Their most important backers are all rich, white men, and their main intraparty opposition (i.e., the teabaggers) are rich, white men. Being powerful, they are surrounded by coteries of yes-men and sycophants.
In this light, it becomes clear and unsurprising that Republican politicians would come to the conclusion that what's best for the rich is always best for everyone. This explains why even the most seemingly conscientious Republican believes the only thing better than cutting taxes on the rich during boom years is cutting taxes on the rich during bust years. It explains why the answer to every problem is "cut taxes on the rich and gut social programs." It explains why every term of Republican dominance is marked by the attempt to destroy either Social Security or Medicare, no matter how popular the two become. It explains why conservatives cannot separate cutting the deficit from cutting the size of government. And it perhaps explains why Republicans can, in the process of creating a budget with the sole and specific intent to cut the deficit, cut taxes on the rich and not see any inconsistency there.
I'm coming around to the belief that Republican politicians vote for Ryancare because it fits their ideological, emotional, and cynical predispositions so perfectly that they have convinced themselves that its premises are intellectually unassailable. If it is unpopular, it is only because its genius hasn't had time to sink in yet.