Let's see if we can make this as fair as possible:

Single moms, when an interesting, caring guy messages you on this, or
some other dating site, and slowly works his way into your life... you
go on a few dates, he meets your kids, etc, and then turns out to be a
pedophile... Well, you get to explain to your kids how it happened.

People are guaranteed a certain degree of anonymity on the internet.
Someone you can see in real life is much less likely to try to prey on
your children. There's no way to tell for sure who is dangerous, they
can give a fake name and make up anything they want.

But hey, they're your kids.