I'm not sure I understand what work "on principle" is doing in this sentence.
What's the difference between voting against anyone who acts against your interests "on principle", and voting against anyone who acts against your interests "out of self-interest"?
(I am not suggesting that you shouldn't vote self-interestedly; arguably democracy works best when everyone does.)
Assuming I understand your question, I vote for people I would not have otherwise voted for merely to spite the people who have harmed me in some way. It's petty but it makes me feel like I have reclaimed some agency against said aggressors.
Candidate A - will do X, Y, Z all in ways I think are the best
Candidate B - will do A, B, C which I prefer less than X, Y, Z but in the grand scheme likely impact my day to day life little.
Candidate A - also supports (or is supported by) people / movements that actively make my life harder and piss me off.
That's not cutting off my nose that's deciding I can live with a less optimal solution to some problems to avoid something that pisses me off massively from growing more powerful
What's the difference between voting against anyone who acts against your interests "on principle", and voting against anyone who acts against your interests "out of self-interest"?
(I am not suggesting that you shouldn't vote self-interestedly; arguably democracy works best when everyone does.)