I should also point out that people genuinely don't know. Yes, parents should be educating their children about such things, but a lot of the time, they don't. My mother is very embarassed about such things, and I think she assumed I would learn it from school.
It also doesn't help that, and I wish I was kidding about this, when I was having Sex Ed in the ninth grade, the teacher stood in front of a classroom of students, held up a condom, and told the assembled class that condoms would fail to prevent pregnancy 75% of the time, and that abstinance was the only way. I can see why people, if this is the only education they get, don't bother. Why use something that is only effective 25% of the time?
Granted, I'm stuck right in the middle of the bible belt, so most places aren't so extreme, but still.
My mother and I were watching Glee a few years ago, and a character pulled the old 'you got me pregnant in a hot tub' lie MOm couldn't believe how stupid the male character was for believing that, and I had to break it gently to her that I went to college with people who genuinely believed that it was possible.
Should people do more research? Yes. I'm not saying that there isn't a lot of personal responsibility involved, especially with the decision to bring another life into the world, but lets be realistic. Once people are told that something is the truth by a person in authority, most of them don't question it. It's human nature.