Elections, especially under First-Past-The-Post voting, are coordination games- not opinion polls. If you can assemble a coalition of ~70 million voters for a third party within the next two months, sure, do that. Otherwise, you are abstaining as far as the outcome is concerned.

It's very easy to dislike both candidates in play today, and certainly feels good to vote for neither.

But they are not equally bad. One candidate views large swaths of Americans as inherently illegitimate, while the other is perhaps garden-variety corrupt.

Your conscience is what stops you from doing things that feel good, but hurt others.