Well first of all, they don't go when they're infants so they can take care of themselves and won't die from neglect.

And second of all, girls are just as good as boys. That's common sense. The top student in my year is a girl. The Headmistress is a woman. Mrs Lestrange is a woman.

Squibs aren't as good as wizards because they can't do magic, and you really can't argue otherwise. You can't. It's one of the basic facts you just have to know going on.