If a champion is being hovered by a player, allies of that player cannot ban it.
I get that we all have reasons for banning allied picks, but if the player intends on trolling anyway then banning their champion isn't going to stop them from doing just that.
And by allowing players to ban allied picks, all we end up doing is enabling the trolls to have further control.
Case in point, three queues in the past two days I've had a player deliberately ban my pick. No apologies were given. One player laughed at me after doing it. And another told me that they were doing me a favor by banning a "useless champion".
Pick intent exists to inform our allies of our picks prior to the banning process so as to avoid having our champions banned by our own team.
But the freedom to ban whoever we feel like regardless of our allies' desires compromises that.
Again, if a troll is on your team, they're going to troll you no matter what you ban. But players who are trying to contribute shouldn't be subjected to hostile treatment such as having their champion banned just because allies don't like it.