A USA Today piece on the declining number of baptisms

Among Catholics, Sullins says, the rate of baptisms has fallen faster than the rate of decline in births.

Baptism isn’t the only source of new members. The church’s U.S. numbers — up from 31.6 million in 1954 to 67.8 million last year — also have grown through immigration. And at Saturday’s Easter vigil, the church will receive tens of thousands of adult converts.

The sociologist also links fewer infant baptisms to two trends involving marriage. Fewer Catholics are choosing to marry in the church, and Sullins says they may be less "attached to the sacraments." And, since a change in church law in 1983, Catholics who marry non-Catholics no longer must promise to baptize and rear their children as Catholics.

Intermarriage slows baptisms

Now the church requires only "a general recognition by the couple that the Catholic partner’s faith will be respected."

"The more you see more inter-faith marriages or couples where one partner is lukewarm or hostile to organized religion, the more you will see baptism taper off," says the Rev. James Martin, associate editor of the Jesuit magazine America and author of My Life with the Saints

"I know friends who themselves are strongly Catholic but who married people inimical to the church, and it’s hard to agree on what they should do with their baby. At the very least, it delays baptism. The more delayed, the less likely it is to happen at all," he says.

I’d add to the mix the issue of second marriages and children born out of wedlock. In both situations, parents often feel hesitant about approaching the Church for baptism, afraid of being scolded or even turned away. But I do think the fundamental issue is found using Occam’s Razor: the reason the number of baptisms has declined is because people don’t believe it serves any necessary purpose. When something like 30% (if that) of self-identified RC’s go to Mass weekly…well, they’re not going to prioritize baptism of their children, for any number of reasons.

The article also addresses the decline of baptism in believer-baptism denominations, with some ascribing it to the shopper mentality that really does not want to commit, but simply to try this style of church for a while, until we move on to the next one in a few years.