Things I don't understand #2

I have been reviewing Constitutional law this week and while I generally find the subject to be interesting, there are somethings I just don't get. So I was reviewing the suspect classes and quasi suspect classes. And the whole concept seems like bullshit to me. Where in the constitution are these distinctions ever even slightly founded? They aren't. And gender and legitamacy are the only 2 suspect classes? Generally, I thought the whole legitamacy shit was over with. Laws are pretty equal on this. I guess they feel the same way about gender discrimination but I am just not buying it. Regardless, could someone please explain to me how 9 people have the authority to decide that different discrimination is entitled to different rules? I just don't get it. Really, I thought discrimination was wrong regardless but clearly, like with so many other things, I was mistaken/confused.