It isn't.
Having children outside of wedlock is because you will create psychopathic children that will destroy us all (raised by single mothers).
Also disease is actually a legit thing that is much more likely to spread via bodily fluids.
Bastards are much more likely to be serial killers / criminals. Not saying all of them, but most. I grew up with a single-mother, it was rough. Not that I agree with them, but I can understand why so many criminals ended up the way they did. So sex isn't in and of itself immoral, but recklessly done, it is destructive.
Not sure what your point is with the other stuff.