1. Many STD's can remain symptomless. So that indiscretion in college, you passed whatever you got from that to your partner.
2. Oral sex with no protection? STD's can pass that way too.
3. Condoms aren't always effective. I'm not saying we shouldn't use them - we definitely should, but condoms can break and they're not always effective... for example HPV (often symptomless) can be present at the base of the penis or the outskirts of the vagina.
4. Having two faithful partners or finding the right person in the first person you sleep with is not the norm, unfortunately. You have to be more realistic that sex happens.
5. Try to refrain from judgements on those who have "screaming brats on the social support system"/have std's/have abortions. You don't know their motivations or what they've been/are going through.
Bottom line is - get tested for std's, get tested often. Think twice before you have sex, and use condoms. And make sure the meds (all of the meds) clean up your junk!
ps. it's not natural selection if they have kids and they survive and also have kids comma.