I absolutely agree that you should be allowed to change your opinion over time, as long as you do it 'honestly'. For example, it bugs me when people lambaste politicians for having a different opinion now as opposed to 20 years ago. But at the same time, by 'honest' I mean being open about the changes and not quietly twisting them or hiding them, which is what Torvalds is complaining about in that video. In the organisations I mention I was part of, the same thing applies - lip service paid to the (sometimes stale) principles, but the behaviour was rationalised very baroquely to fit those principles.

Re: the idealism stuff, my armchair psychology take on it is this: conservatives are passionate about things not changing, so minor differences don't matter so much because the overall goal is the same; progressives are passionate about things changing, so if the cart is going to move at all, it really needs to go in my direction. Add in the human predeliction for not seeing the forest for the trees, and the progressives will squabble over what really are minor differences.