I was raised Catholic, but I reject the ideology completely now because of their stance on transsexuals. It goes something like this: your body isn't yours - it belongs to god. Therefore you shouldn't 'modify' it.
I sometimes wonder if the Catholic Church would take the same line if I told them I intended to 'gift' a kidney to someone. Somehow I doubt; I think they'd be completely cool about me 'modifying' my body to save someone else's life, but if I need to 'modify' my body to save my own life, it's a no-no. F'king hypocrites!