There is an old joke to the effect that anyone who would voluntarily run for public office should be automatically disqualified from doing so. It's easy to see why this has resonance with a lot of people, because the kind of person who seeks political power very often is exactly the kind of person who shouldn't get it.
I have to admit I share this general prejudice, although for me it is directed more at political parties than individuals. I have a strong disdain for partisan organizations for a variety of reasons, and so when someone says, "They're all a bunch of crooks!" there's certainly a part of me that wants to shout "Amen!" And I certainly share the desire to wash my hands of the whole thing and just walk away from it.
And so I am sympathetic to those who either decline to vote or who deliberately spoil their ballots in protest, as a way of saying “None of the above!”
But here’s the problem: there is no “none of the above” option on the ballot, and practically speaking, abstaining or spoiling your ballot is identical in effect to voting “all of the above”. One of these disreputable nogoodniks will be elected; the only way you could possibly frustrate that by not voting is if absolutely nobody else votes, either, but the fact that there are candidates who have taken the time to get nominated and run means that at least they are probably going to be casting ballots. The one who ends up with the most votes will win, regardless of how tiny the actual number of votes might be, and the fewer votes cast, the easier it is to get the most. So, by not voting, you are in effect actually tacitly accepting whoever it is that eventually wins: you may not have voted for them, but you did not vote against them, either.
There really is only one way to vote against a candidate, and that is to vote for a different one. To put it another way, if six zombies are attacking, you only get five bullets. (Also, in our first-past-the-post system, you don’t get to shoot twice at the same zombie.) There’s always going to be at least one you don’t shoot at; choosing not to vote just means you don’t shoot at any of them; you think you’re expressing your disgust for all the zombies equally, but really you’re making it easier for them.
Which is another thing. A lot of people, in throwing up their hands in disgust, say “they’re all equally bad!” But that’s not actually true. There will almost always be some variation in degrees of badness, and saying they’re all the same works to the advantage the worst of them, and to the disadvantage of whoever might be marginally better than the rest. In other words, by treating the worst as if they’re as good as the best, there’s little incentive for anyone to improve. Remember: declining to cast a ballot is functionally identical to voting for everyone.
Now, you might think that I’m arguing in favor of voting here, and of course I really would prefer it if more people showed up to vote. But in fact, I really have nothing against your choice not to cast a ballot. By all means, abstain if you want, but only if you are really and truly indifferent to who eventually wins.