Well it kind of is. Even more so I'd imagine if you're an atheist. Surely?
If you are baptised as a Catholic then your name goes on a register of Catholic people. The more people on the register the more power the Catholic church has. I don't know if you realise how powerful the Catholic church is and just how much they manage to control, how much influence they have on politics etc. Being baptised into a religion wether you believe in God or not associates you with that religion and all that they stand for. I will not have my daughter associated with the Catholic church unless she is old enough to choose for herself. It's got nothing to do with my religious beliefs.
Pretty certain that this is not the case in the UK, and Catholicism isn't even our state religion and has only as much power as other faiths. Here religion is counted by what is put on a census.
Anyway, like I said before, a lot of Catholics accept that anyone can baptise. Doesn't have to even be in a church. So no association there.