By counsel,
By command,
By consent,
By provocation
By praise or flattery, (how do you attend a wedding and this one doesn’t come into play?)
By being a partner in the sin,
By silence,
By defending the ill that has been done
Doubt that his mom said “Son, do you think I should be a lesbian?”, scratch counsel
Doubt he commanded his mom “Go marry that woman!!”, scratch command
Doubt he said “I double dog DARE you to marry a woman, you are a coward if you do not!”, so, no provocation.
Doubt that he is saying “mom, you are the BEST lesbian in the world. You put all of the other lesbians to shame. And this wedding, it makes all other lesbian weddings pale in comparison!!”, scratch praise and flattery
Being a partner? Just ewww
Silence? Nope, he has already said that he does not agree. And I’d bet you his mom KNOWS that the Church does not believe lesbian marriage is valid.
Lastly, defending. Again, cannot see the poster above defending the wedding. Sure, he would defend his mom and that is what a good son does!
I wonder, if the poster were asking if he should attend the wedding of his mom to a divorced man outside of the Church, would he be so barraged by the choir here?