He probably thinks it's okay to do that because of SOUTH PARK, but there's something about the way they use those words that makes it different and sometimes necessary to make a larger point--and they make a point of being genuinely pro-gay rights(and gay marriage) as well; nobody can mistake Parker & Stone for homophobes.
When Way does it, I suspect he does it maybe because he thinks it's just okay to say "fag" now. I understand Ennis is an influence of his? Ennis would never use it that way.