Tax evasion is a crime. Tax avoidance—legally reducing your taxable income—is good and more people should learn about it. You shouldn’t unnecessarily “compensate the state” for things you don’t want it to do.
there’s some amount—your donations—which is allocated according to your flavor of expected impact; and another one—taxes—that’s allocated by democratically chosen representatives in your country
This is right, and you should just minimize the amount you allocate to the state, whose effectiveness is very low.
For what it’s worth, my experience at EAGx Boston two weeks ago was in line with this comment I remember from How Effective Altruists Can Be Welcoming To Conservatives:
I remarked to some friends while leaving that I had never met so many people so left-wing whose eyes lit up with enthusiasm when I mentioned that I was interested in Republican party politics. Cause areas related to X-risk, foreign aid, etc. are relatively bipartisan.