Voting One's Conscience

(I post this here instead of GDP because it is about the GE and only tangentially related to the primaries)

I've seen a lot of comments, here and there about the Web, ringing changes on the theme that "conscience" will not permit an individual to vote for this or that person in the GE, if the preferred candidate fails to win the primary. With deliberate intent to keep personalities out of the question, I am puzzled by one thing.

Mr Trump is the presumptive GOP nominee for the GE. (Obviously not a done deal, but for the purposes of this post, let's consider that he will, in fact, represent the GOP in the GE) He has already promised to persecute Muslims and Mexicans, suggesting registration and special insignae for the former, and shipping the latter to the border in cattle cars for expulsion. He has openly advocated the assault and battery of those who oppose him; his encouragement of supporters to inflict violence upon protesters is a matter of public record.

If one's conscience will not permit a vote for a Democratic nominee who does not embody the principles one holds dear, my question is this: how does that same conscience allow one to not vote against the principles embodied by the GOP candidate?

-- Mal