The author is correct. No one, Christian or not, should attend a same-sex wedding.
I’d go further than just not attending a “wedding” between two such people. I would not generally associate with them socially or in a Christian cultural context. We are told in Scripture to “turn away” from “such as these.” Open, proud homosexuals have reached a level of lifestyle blasphemy that can’t go much lower. They epitomized every condemnable characteristic mentioned in 2 Timothy 3:1-5.