I haven’t read the thread yet, but I thought I’d offer my perspective.
To some, this is just a matter of principle, even if it’s ultimately against their best interests. I, for example, am for estate taxes even though I stand to be an heir of a taxable estate. It would be in my best interest if estate taxes disappeared. I’d get more money. But it isn’t money that I particularly want or need, and the only thing I’ve done to “earn” it is not be a total shit to my mom. I think, honestly, that there are better things to do with money than hand it to your kids, but I don’t have all these illusions about myself that if I had someone standing there giving me a check that I would piously wave it away and tell them to give it to the lepers.
(One of the reasons I think taxes are effective is that they can be decided on in rational moments and then the decision doesn’t have to be made every minute of every day.)
So, people can simply decide the principle of something is more important than their personal gain from it.
I think there are other people who are for tax cuts because its in the platform of the party they have chosen for other reasons. It takes more to deviate from your party on any one issue than it does to go along with that issue. When you’re a Democrat around Democrats, you’re assumed to have beliefs X, Y, and Z. When you’re a Republican around Republicans, you’re assumed to have beliefs A, B, and C. If you have beliefs that are outside the mainstream of your party, they might drift into the mainstream through the sheer amount of repetition or expectation you encounter.
So, if you’re a Republican for social issues, you could end up defending Republicans and Republicanism, and eventually embrace what you’re defending. It’s psychologically easier.
It’s easier to be an anti-gun Democrat than a pro-gun one. It’s easier to be an anti-gay Republican than a pro-gay one. There’s nothing inherent to the DNC or the RNC that makes this true, only the sheer weight of all the members for whom it IS true.
Then you just have your fools and your damned fools, or maybe I already covered this when I talked about self-harming principles.