You only abort unwanted children - if you’re using contraception anytime it fails, all children are unwanted. Ergo - contraception changes the mentality.
Most abortion clients were not using contraceptives at the time they got pregnant. Thus, even though they may not have wanted the child, it was still a planned pregnancy.
A little bit of education about pregnancy would go a long ways towards combatting the attitude that it's okay to be irresponsible because everything can be "taken care of" via abortion.