Having sex without condoms almost guarantees that a pregnancy will arise, as no pill or IUD is 100% preventative. Also, with IUDs, there is a very high risk that said pregnancy will be endoscopic, meaning that the zygote will implant itself onto the walls of the fallopian tube instead of waiting until it's in the uterus. This is not only dangerous to the woman, but painful and scary as all hell.

It's also very foolish as the risk of getting STDs goes through the roof. The Pill and IUDs don't have any shred of protection against these. If you have any shred of common sense and don't want a baby in the near future, or want a lifelong illness, then the use of a condom is very much mandatory.