FIRST describe to me why either of those issues (abortion, marriage) belong under federal purview. (Both existed when the Constitution was written, and according to that irrelevant thing called the Bill of Rights, if it is not expressly granted to the Federal level, then the issue automatically reverts to the states.)
THEN we can discuss why a national party needs a stance on either. Sadly, our national representatives don't even bother with the preliminary "is this under our jurisdiction" question anymore. Sad.
But then again, I'm not welcome in your party, so what do you care?