The Bible teaches clearly that homosexual behaviour is sin. The orthodox moral teaching of the Church for 2000 years teaches that homosexual behaviour is sin. How is 'affirming' homosexual behaviour then 'Christian', when such 'affirmation' rejects the very foundations of orthodox Christian teaching? - It is, of course, not Christian in any substantive sense of the term.
Those church goers who lie to themselves about the 'Christian' goodness of their homosexual behaviour are also lying to everyone else.