One of the reasons put forward by some conservatives for voting for the controversial Republican nominee is that not voting for him would be “a vote for Hillary”. It’s important to understand why this is a really bad argument.
In the first place, the claim itself is inaccurate. If there are only two candidates, A and B, and Oscar doesn’t vote for A, that could mean one of two things:
(1) Oscar votes for B rather than A.
(2) Oscar votes for neither A nor B.
Clearly these aren’t equivalent, because (1) hinders A’s chances of winning more than (2) does.
But it’s worse than that: the reasoning here is incoherent, because if a non-vote for A is a vote for B, then by parity of reasoning a non-vote for B is a vote for A, from which it follows that not voting for either candidate is voting for both candidates. On the most charitable interpretation, that simply means not voting at all would be neutral with respect to the candidates: it wouldn’t favor either of them. On a less charitable interpretation, it’s just a nonsensical conclusion.
Perhaps there are some good reasons for conservatives to cast their vote for the Republican presidential ticket in 2016, but this isn’t one of them.
Addendum: I should add that the same incoherence afflicts another popular argument, namely, that not voting would “allow Hillary to win”. If a non-vote for A would allow B to win, then equally a non-vote for B would allow A to win, in which case not voting for either candidate would allow both candidates to win, which is absurd. (Actually, the conclusion in this case could be interpreted somewhat more charitably: not voting would allow either candidate to win. But again this just highlights the neutrality of a non-vote.)