I know lots of Muslims who drink and Catholics who take contraception, but are pretty devote in all other areas. Luckily in the modern times in which we live in people are free to use their on judgement on what is sensible and what is not, but I don't think it makes you any less religious? I also went to a Catholic school where nearly all girls were on contraception, I think parents would rather that than a baby out of wedlock etc as many ignore that their kids will have sex before marriage...