I agree it may be the only practical way to do it in a lot of cases, but what about when you run into something that is justified by the religion, like a man beating his wife or considering a woman's court testimony inferior. The only way to remove the reason is to remove the religion - trying to reform it from within is like saying "don't throw out the baby with the bathwater" when there is no baby.
The history of religion (in general) doesn't support that - religion can be seen to have often followed changes in societies and cultures and changed or entirely reversed or dropped their religious beliefs as a result of that societal pressure.