Allow me to sort this out - Voting on principle, when you know your vote will not effect the outcome of the race in question, is a symbolic action and not a wasted vote. There is nothing wrong with symbolic actions, they are often noble. Likewise, voting for the lesser of two evils is not a cop-out. It is a pragmatic recognition that the future matters, and will be partially determined by the election at hand, so a side is chosen.
Those who can't decide whether to not vote, to cast a symbolic vote, or to vote for the lesser of two evils should ask themselves what impact the symbolic vote will have because such votes have, at times, been noticed. Then they should weigh against that whether their vote for a viable candidate can make a difference. Does it really not matter at all who is elected? Not at all?