Alcohol prevents you from thinking completely logically as if you were sober. Under the influence, you might possibly end up the victim of someone asking for sex or pushing themselves on you without you consenting. You can't truly consent under the influence, so that leads to sexual assault. Among this, someone who is trying to take advantage of you under the influence may carry STD's, so by them having sex with you, they can transmit said STD's. They could also refuse to wear a condom, either because they're under the influence alongside you, or they know that you can't stop them.
