Earlier quoted context omitted.
for the same reason someone against marijuana legalization is anti-marijuana Thats the political stance directly opposed to support.
That sounds like a false equivalency to me. How is being against gay marriage being against gay people? As far as I'm aware, there were a certain amount of gay people who didn't want gay marriage either. Are they anti-gay?
the answer to both questions is yes - people can have conflicting ideologies.
Being against giving someone (or something) rights is politically equivalent to being against that thing.
If im a proponent of black people not having the right to vote, am i anti black or do i just think people shouldn't vote?