Would someone explain casual sex to me, please?

I’m not asking about morals. At least, I don’t think I am. I’m speaking logic here.

Let me also say I’m no prude.

But one thing I have never understood is people having sex with people they don’t know very well. Or don’t love. Or are unwilling to potentially be tied to for the rest of their lives.

I get meeting someone really hot at a bar. I get having a connection with him/her. I get the desire to kiss, make out with this person. The point at which I stop understanding is the actual act. Because then you introduce all kinds of crazy risk, right? You could have a baby with this person!! Or worse …

Safer sex

I understand condoms are highly effective. That is “safer” sex. But I asked a friend this, after he argued that point with me: “Would you have sex with someone who you knew had AIDS if you wore a condom?”
“No,” he said.
“Why not?” I asked.
“It’s not worth the risk.”
“But, you said condoms are 99% effective,” I answered.
“I see your point,” he said.

False security

My friend says it’s possibly a false sense of security that leads people to just jump into bed with each other on first dates or after a fun night at the bar. He sent me this article to illustrate it. Does this mean teenagers are smarter than we are?

I hope I don’t sound like I’m on a soapbox or a prude. I really am curious – to me it seems as if the risk greatly outweighs the benefit of casual sex. So how come so many other people seem to feel the opposite? What am I missing?