First contact often happens during intoxication with alcohol or other substances (like weed, etc). For some it might sound ok – there’s no stress and psychological problems. With the effect of alcohol all walls come down, sexual drive increases and you can have sex whatever place. And if this “drive” is enforced by certain company where everyone is bragging with “experience”.
Often in such companies girls loose their strength of resistance and games with undressing might end up with unplanned sex, group intercourse or rape. In such situations nobody thins about contraception of course. Not mentioning a mental trauma. Remember that during intoxication with alcohol you do things you would never do when you’re sober!