@Steve: I know it's not my business, but I'll try and tell you something about your current religious predicament.
On one hand, I appreciate your effort in being consistent with your personal resolutions: you're willing to suffer in order to affirm the fact that if you don't believe in God, you shouldn't be forced to go to church. As a general principle, being able to withstand exclusion, violence and displeasing situations on account of one's ideas is good.
On the other hand, I've found out in time that there are not many circumstances that call for dogmatic defense of one's positions. From what you tell us, you have a certain latitude: your mother attacks you because you don't go to church, but you're free to have a messy room (when i was your age, that was not allowed in my home), you go around and steal stuff (christianity has nothing to do with the idiocy inherent in stealing when you don't need to steal), and so on and so forth.
I believe that you should give your mother a break. Ok, she should not try and force you to worship, because spirituality is a very personal part of life and everyone should be entitled to their own search for truth. On the other hand, she feeds and shelters you, lets you be as unkempt as you want, and is pretty lax in prohibiting your use of UM, since you seem to be here on a regular basis. For the sake of honesty and consistency (also saving you from the hypocrisy of catholicism, certainly one of the reasons why you refuse it), realize that you're not the boss since you're not the breadwinner. Try to be decent and don't tell her to fuck off on account of her religious beliefs. I'd even go to church, in order to show a bit of gratitude for the family that still keeps you, and maybe try to discuss spirituality and freedom of choice in a non-heated setting. One day, you'll grow up to be an independent man with a salary, a home, and maybe a family of your own. Then you'll decide if you want to go to church or not and nobody will be able to challenge your decision. Still, you won't like it should your kids rant about the bloody stupidity of atheism (or agnosticism).