I like the idea for one reason in particular: So you don't get the kind of person who just bans who you want to play.
Seriously, it's happened twice to me, so I've stopped answering. They ask who I plan to pick, I think they're asking to help complement the choice, then they just ban them right away and laugh at you about it.
That should be its own category for reporting. That's such a horrible way to kick off the next 20 minutes with someone who has no intention of helping his team, just making it as miserable as possible because it's funny.
These people are the worst scum of LoL. You show them goodwill and faith, and they laugh at you for it. And no one on your team can do anything at all about it except sit through the next 20 minutes. How there is no vote-kick option, or any option to deal with someone whose sole intention is to make his team sorry to be there, is astonishing. It's staggering that this and other pre-game issues (e.g., people who never connect from the start, people who don't approve of your "noob champ choice because they suck" and are hopelessly toxic all game, or people who didn't get the role they wanted so they either feed or go afk right away) hasn't been dealt with in any preventative way, just reactively, after the damage is done. But that's a tangent beyond the scope of the thread, so.
So, if only to prevent that from happening a third time, I'm all for it. But I also realize its fairness, of course, so I'm for it in that way, too.