If you buy into a the lipservice a lifelong supporter of abortion who even now defends Planned Parenthood and is a recent and politically expedient "convert" to the pro-life cause- one who didn't even see fit to mention abortion or other social issues in his acceptance speech, and seems to lean Left on most of them in any case- you are not simply being personally played for a fool.
You are serving notice that no future candidate need take abortion or the other concerns of conservative Christians seriously. You are signalling that hypocritical lip service is enough to buy you off. You are destroying any possibility that our votes and voices will have any influence in future elections.
Why vote for what is dubiously said to be "the lesser of two evils," when you can stand up for what is good?