So...by working the party he would be giving his implied support to birthdays?
The supposed customers went looking for trouble by declaring it a "gay" birthday party....with a stress on the "gay".
Not to birthdays but to the lifestyle of the participants.
Working the birthday party makes him a participant in the party which would mean he condones the lifestyles of the participants.
By condoning by participating he is breaking the law of God.
When Moses was on the mountain receiving the law from God, there were those who didn’t condone the worshipping of the idol.
By *not* separating themselves from those who did worship the idol, they were as guilty as the active participants.
God condemned the Jews to wander the desert until that *entire* generation had passed away.
The law of God is narrow whether we like it or not.