I actually agree with you. But I would like to state that there is a difference between "refusing to vote for (insert office)" and "refusing to vote at all" - I also used the word "often", implying that it is not the sole reason people refuse to vote.
I could not in good conscience vote for Clinton in 2016 - but I was lucky enough to live in a deep, deep blue state at the time, so my writing in Bernie in 2016 had no impact on who won. But I also still voted down-ballot. I felt that people only liked Clinton insomuch as she was "not Trump" and I feel the same is happening with Biden. As long as the most important aspect of a candidate is that they are "not that other guy" then nothing will ever get better in this country. People need to stop spending so much time worrying about who their neighbors will vote for and spend more time choosing a candidate that they actually like themselves. As you said, there's got to be a line somewhere. I think for some people that line was Bloomberg, and while I'm glad we dodged that bullet I'd have been interested to see what would have happened.
We really need some kind of ranked choice voting system that would allow people to vote their conscience without worrying that their vote will allow the greater evil to win. I'm personally sick and tired of being forced to make this idiotic choice between two evils every year. Instead of always voting against something, I'd really like to have something to vote for, for once. I'll be there on Election Day, but I'm not excited anymore - it'll simply be a civic duty again this year, as usual.