Where else do people boo?
Why is it considered a thing to do at the footy? Where did it come from?
You dont really see it at any other sport - tennis, maybe - but cant imagine a bunch of people following a golfer around a golf course booing his every action.
You dont see it in society in general - i've never seen anyone boo another person walking down the street, i've never seen it at school, university, nightclubs. The only thing i can think of is a protest - but even then people can usually manage to string a few words together to express themselves rather than just make noise.
Yet here we are with a bunch of people trying to justify themselves with all sorts of ridiculous reasons why its ok to incessantly make derogatory noise at a person for a good three hours every weekend.
If you want to boo, for whatever reason, go ahead.
But IMO, why not come up with some words to use, make yourself look more intelligent than an angry caveman.