Quoted because I can't say it any better.If your exhaust is loud enough to scare the shit out of pedestrians or making people roll up their windows just to hear themselves think...then you're being an azzhat!
I drive a diesel dually. Sure I can tune it to fill every intersection I go through with enough soot to block out the sun, but I don't. Bikes with loud exhausts are just the biker's equivalent of rolling coal. Nobody likes those big lifted trucks rolling coal at every intersection and stop sign, except the guy driving it. And nobody likes big loud obnoxious bike exhausts, except the guy riding the bike.
Because I live in a world with other people, I try to be as non-intrusive as possible. It's not because I care what other people think of me. It's because I don't want to live in a world where everybody is as abrasive as possible. I want to live in a world where people are as helpful and considerate as possible. To accomplish that goal, I have to be as helpful and considerate as possible. Making my vehicle so loud that it's heard a mile down the road is antithetical to that goal.
Now I understand wanting to make your bike your own. There is absolutely nothing wrong with that. Mods are wonderful and I highly recommend looking into them. But if half of the vehicles on the road were bikes, and half those bikes had a loud obnoxious exhaust, you'd be sick of that sound and complain that you can't hear yourself think. That's what your big loud exhaust does to everyone that can hear it.