Why is a team mate allowed to ban another team mate's declared champion?

Because some people doesn't want to lose ranked game only because Camille was released 2 days ago and no one knows how to play her yet.

I wish the community could communicate about these things rather than simply banning a champion someone hovers. By doing this, you intentionally piss off a teammate and the game starts with people tilted. The argument of "I ban X champion because I don't want a teammate playing them incase they suck" isn't a viable excuse. Especially if that individual is immature about the situation and decides to troll in the game.

Because the alternative is worse. People could troll by indicating op broken champs then giving them to enemy team by not picking it.

Because you have to be able to ban yasuo even if a teammate hovers him.