[Sunlis]

Putting scare-tactics on cigarette packaging works because the person buying them is "in the wrong" and needs to be "scared away". Negative reinforcement to make an action or habit less desirable.

I'm no psychologist, but I would guess that associating the scary images of STDs and the like directly with condoms and contraceptives in general would be more likely to cause people to form a negative opinion of condoms. What you want to do is advertise sex and condoms side-by-side, so that thoughts of sex trigger thoughts of condoms, rather than thoughts of condoms triggering thoughts of STDs and child-support. Positive reinforcement rewarding positive behaviour.