Because it's simply not a suitable place for an animal that can be unpredictable under stress. You dog freaks out because of the stress of fireworks, large crowds, strangers, new place, etc. and suddenly flips the script. Not a bad dog, but an idiot owner. Your dog bites someone. Now what?
Unless you're willing to accept having to pay 700 bucks to kill your dog afterwards and pay whatever costs come from any treatment for the victim, and be barred from pet ownership, don't bring your animal to public events for humans.
I hate this argument "my dog is nice" TO YOU.
You missed the entire closing sentence. Your dog is good to YOU. A public event is not a place for pets. It doesn't matter how well you know your dog because your dog doesn't know a stranger.
Adding to that, if your dog bites someone are you okay with taking to the vet and paying $500 to kill it? Are you okay with taking the blame entirely and potentially getting your shit absolutely wrecked because of it?
This is such a stupid conversation. A dog is a possession. You own it. This like asking if you can bring a knife or gun to a fireworks show, it just doesn't make sense. Both those two things are infinitely safer than a dog because you can predict what they'll do.
What is wrong with people?