All of you are saying the same thing in different ways. Regardless of the rationales, IMHO it IS a waste of your vote in a Presidential election. Not even the explanation Lord Tammerlain mentioned in Post 8 is a valid excuse, because there is no real way (as was found in 2016) to be sure that polls were right.
No one is ever going to be absolutely everything you want in a leader. NO ONE. This is why after trying Dem., Rep., and finally Libertarian, I became an independent.
The best you can do is pick the candidate you think has more stated policies and goals that you agree with than not, and whose history shows this is more likely true than not at election time.
This is not the case for Congressional and State/Local elections because those candidates directly affect you and you can literally "reach out and touch them" when they have office hours in your locale. Your vote really counts at that level to them, as does your activism.
But the President isn't that approachable, not even during campaign stops; nor is he focused on purely local concerns. A Presidential candidate is trying to reach as many people as possible across all sorts of national needs and desires. Yet that candidate will have a history, and a platform some of which you can likely get behind.
So IMO it is really important to make a valid choice when voting for President, even if it means picking the lesser of two evils. Voting "your conscience" accomplishes nothing if it is directed at a 3rd Party candidate you know has no chance of winning.
The stakes are too high. By letting a candidate who might do more harm to your goals than not get elected, as opposed to voting for one who you might not completely agree with, but is more likely to do things you want, is just passing the buck.
Vote however you wish, but it is disingenuous to assert that you bear no responsibility if you find that what you consider the GREATER of two evils ends up getting elected.