I think it can be either, depending on the given election.
If neither candidate is worthy in one's eyes, and both candidates are roughly the same, then I see no issue with not voting. I would view not voting in this case as a form of protest, but I'm fine with that. I think that's valid.
If neither candidate is worthy, but one candidate is far worse than the other, then as unpleasant as it may be it is still beneficial to vote for the "lesser of two evils" simply in an attempt to keep the "greater evil" out. It's not ideal, but it's practical self-interest.
Having said that, regarding the person who NEVER votes on literally anything ever, they have chosen to allow others to choose for them, and thus have morally forfeited their right to complain about the results. (Not saying you do this, but some people do... my mother being one of them.)
I'm assuming you are talking about non-presidential elections, then, because presidential elections have little to do with individual votes of the
vast majority of people. Take me, for instance, I live in Illinois.
The outcome of the presidential election is already decided here, regardless of how I vote, well before the election ever happens. If I vote for the winner, it'll make no difference, if I vote against the winner it'll make no difference because very single one of my state's electoral college votes are going to a predetermined candidate based on teh political views of the peopel in my state.
As far as never voting goes, you really need to know what a person's beliefs are before you can claim they have morally forfeited their right to complain about the results. I believe that the two parties are
identically bad for the country. Nether one is superior to the other, and all candidates from either party suck and are essentially pushing the same crap, just with different decorations. This carries over to pretty much every candidate from one of those two parties. Any candidate
worth voting for will never make it out of the primaries because they are, by virtue of being good candidates, going to reject the nonsense from their party enough to sabotage any chance of getting the nomination for that party.
If someone flat-out rejects the two-party system and thinks that any candidate that is a part of that system is, for all practical purposes, equally as bad as any another one from that system, then they are morally obligated to
not vote. They have forfeited nothing, because they oppose the entire system.
Granted, I will often cast a vote for a third party candidate for president knowing the following reasons:
1. My vote doesn't count in Illinois regardless of who I vote for
2. A vote against the two-party system can actually count for something by way of voicing opposition to that system.
3. If enough people vote third party, it increases the chances that third party candidates will be invited to the debates. Even if they don't win, some of their ideas that break away form teh two-party mold could take root.
In local elections, it's different. I will sometimes vote for the lesser of two evils because, frankly, Chicago is a borderline one-party system.