can we please make it so

No because what if you are last pick and you are trying to play a very popular meta/OP pick. Unless you have some one to first pick it for you, it's better off to just ban the champion so the enemy team does not get it first. Now if the champion you are trying to pick isn't very popular or not a champion that is really contested then that is your team being an ass. In cases like those I could understand, but if anything Riot should make a pop up warning you that you are about to ban a champion that is highlighted by an ally.

can not be banned by your own team?

No thanks. I'm definitely banning out that top lane bard.

stay bronze

It already shows you that a teammate is hovering the pick, when you go to ban it, that's enough.

There's a few dangerous scenarios that can happen if you make it so you can't ban a champion an ally is hovering, which is why I don't think it's a good idea.

The first happens when there's an OP champion of the patch (be it a champion with an exploit or an item synergy that's insane, we've seen both). Someone queues as Fill for the fastest queue they can get, hovers OP champion, and says they'll only let the team ban it if someone swaps them their preferred role. This would be frustrating to deal with, a team being 'blackmailed' because they couldn't just ban a power pick.

The other abuse scenario would pretty much be exclusive to scripters, but could still cause problems. It'd be fairly straight forward to make a script that auto changed their intended pick to whatever champion you're hovering before you could ban it. This would force you to dodge, potentially costing you LP or pushing you into a Low Priority Queue.

That's not to mention people who are crazy enough to think that a newly released/reworked champion should be allowed in Ranked for the first patch.

So no, I'd rather retain the option to ban ally champions should the need arise.