It is my view that, in terms of importance, for most people, the ceremony is more important than the religion.

For that reason, I go.

I avoid them.
But I don't have any religious friends or any family so it isn't difficult.

This is difficult, as you say, especially if it's family. My brother, who I'm really unclear on regarding his actual belief. I THINK he is a believer, but definitely not religious. His wife, however, is Catholic, and has raised their children as Catholics. They are rather hypocritical because none of them attends church, but they have the other bases covered, if you will. I think it was their children's confirmation we were invited to. We went in support of the family, but now I'm almost militant about my atheism and wouldn't agree to going to a similar event. Weddings are another matter. I think a lot of people just defer weddings as the purvey of churches. Neither of my two weddings were held in churches, nor were they religious. We wrote our own vows and used nondenominational ministers.

To your point, in the case of child or adult baptism, I think you could politely decline by saying you appreciate that they have thought to invite you, but as a non-believer, you feel your attendance at such an event would constitute an endorsement or other religious-based support so you'll be unable to attend.

Weddings and funerals of family members only..

Booooring