Yep, I've always found this retort of 'voting anything but Labour is a vote for the Tories' to be painfully reductionist and frankly condescending. The only basis behind a genuine democracy is to vote for who you think is right, not who is the least awful. I don't want to vote for a Starmer led government, but that doesn't mean I'm pitching in with the Tories either.
Abstention is also a virtue of democracy, while the consequences might be extremely unfortunate, so would my conscience being held culpable for directly propping up someone who I'd always hold in contempt. At least I'd have control over the latter.