A vote for a candidate is not an unqualified endorsement of the candidate.
There are plenty of people I've voted for, even though I don't think they have great character and/or have done shady things in the past and/or have shown poor judgement on some issues.
For instance, my present city council member has had an extramarital affair with one of his staffers, but OTOH he's something of a visionary as far as city planning goes. I would vote for him again, despite the fact that his actions were deplorable.
Aside: my views on this used to be closer to yours. As years went by I became convinced that withholding my vote was not sending any message (in a Turing sense, principled apathy looks a lot like mere apathy, and may indeed lead to it). Witnessing some very, very close elections was also a factor.
When people mistakenly believe that they have to vote for one of the few options given to them, candidates only need to seem decent enough to possibly edge out the others. As different people value different priorities, this inevitably results in a race to the bottom. The only winning move is to not play.
I won't be fooled into thinking that steering the 5% of difference between candidates is worth endorsing the common 95% that is never up for discussion.