Same as @Mike_from_NJ attending a relative’s baptism even though he is an unbeliever. His relatives likely know that he does not agree with baptism or believe in God, but he was there for his relative.
First and foremost, I commend Mike for being forthcoming in his ideological position.
Moving along, with all due respect, using his (and non-catholic friends) involvement as an analogy does little to prove you point. Of course non-Catholics are welcome to join us in celebration of Holy Mass and Sacramental occasions! If nothing else it is a form of evangelization, it exposes people to the fullness of truth. Now, if abuses are occurring…e.g. the liturgy is skewed to minimize risk of “offending” a non-believer, or telling a non-Catholic that it is ok to receive Communion, or, in Mike’s case, offering him the task of serving as Godparent… that’s a different matter. I see no indication of that in your post. Hence, it is a joy to share our faith in such a manner.
What you are proposing, on the other hand, serves to draw people away from the faith… away from the fullness of truth (as Catholics know it.)
I guess I personally don’t see attending the wedding as an automatic stamp of approval.
And here, we must simply agree to disagree
Especially since the daughter is not asking for mere attendance, but active participation and facilitation/promotion (with guest list) of the event.
Make no mistake, I respect and understand the challenges of this dilemma. Believe it or not, I’m not trying to be the jerk that sometimes there is no way around sounding like…
Isn’t there something about the letter of the law vs the law of love?
As I suggested before, The law of love entails charity and truth. One without the other makes love not.
I will leave it at this, have this discussion with a priest… a good priest. I am a nobody, so I understand that this is the best thing that I can advise you to do. Be well, and trust in God!