Why would you be interested in voting for someone that moves their positions on issues that you agree with, just to get your vote?
A true denunciation of prior beliefs can represent a sincere change of mind.
If I had to choose between voting for Hillary, for some Libertarian Party candidate, for some Constitution Party candidate, for no one, or for some Republican who has come around to pro-life, pro-gun, and pro-family, then why would I be such a stubborn cuss as to let Hillary win?