DOShea,
The question may very well be “teenage,” but it’s a shame you’re not at all interested in conceptual analysis. The reason I ask them is to get a tad more clarity on the idea of “celebrating” a “deed”—I don’t actually have any intention of drawing practical conclusions from them (e.g., “Tommy and Jim are getting married and having a reception after; since I’m Catholic, I’ll tell them they’re sinners by not going to the wedding, and I’ll tell them they’re friends by drinking with them after.”)
This kind of clarity in necessary because there are many ways of construing actions. You brought out a lose-lose description, and above I brought out a win-win description. If we had any kind of clarity on where Catholics should stand with regard to “celebrating” same-sex “marriages,” it would be possible to decide which description is correct.
Looking at this systematically, there are two distinct dangers of attending a sinful occasion. One, you can be seen as supporting it, by whomever, which has many evils in itself, such as that causes others to confuse the elements of our doctrines, makes Catholics to appear as hypocritical, encourages sin in others (“if Bob is here, and he’s a super Catholic, that must mean its ok”) etc. The second danger is that one is morally culpable (i.e. is sinning) by attending.
Applying the first danger to a reception after the ceremony, it seems the dangers are similar. The purpose, presumably, of a reception is a celebration of the ceremony–that is certainly the case in straight marriages, at least. The newlyweds are the guests of honor. Thus, the ceremony “honors” the guest. The attendant dangers of being seen at such an occasion are equally present.
Now, one might say, we should not do all things for appearances. Perhaps our duty to love the couple in this situation is more important than the duty to uphold a righteous image–surely this is often the case. So the next question is, is the act of attending itself sinful? For if it is, then attending cannot be both sinful and loving (we are called to treat our neighbor as we would wish to be treated; we should not wish anyone to sin on our account.)
Surely we can sin in an act, even if we do not intend it to be a sin (but intend to act). For instance, if I serve or take communion at a non-Catholic church, I am sining because I am acting
in communion with a church that is not my own, not the true Church. This is true even if I do not intend the act to be a sin, and even if I intend the act to glorify God.
I think the same thing applies to attending an illicit ceremony, or a reception afterwards. We are symbolically expressing our solidarity with the lesbian couple and adding our voice to the celebration of the event, just as someone who attends a heterosexual wedding reception is adding to the celebration of the event–imagine a wedding reception where no one attends but the couple. So, just as we can symbolically commit a sin by acting in communion with a church that is not our own, we can also symbolically commit a sin by expressing solidarity with, and adding to the celebration of, an illicit act.
This notwithstanding, as others noted above, we have a great duty to avoid even the temptation or means to sin. Christ said it would be better to cut off our hand than allow it to be a means towards sin. If there ever was a tempting situation, surely a celebration of sinful activity is one. It is so easy to adopt the group mentality and enjoy the wedding while at a reception, if for no other reason but to fit in. Maybe the Catholic in question is extremely firm in his or her faith and convictions, and this is not a problem; but to risk it, merely to show love to the people committing the sin, seems like a reckless choice.
Further, it remains to be shown that attending would actually be loving. If I were lost down the path of sexual sin, would I want someone coming to my reception, acting as if everything were ok? Or would I want someone to abstain completely, causing me to think about why the person chose not to show up? With an unclear at best benefit, and a real temptation to sin at the least, attending such a reception does not seem like a good choice for a Catholic.