Yes, I agree that it is normally rather unsportsmanlike to ban a champ that a teammate wishes to play.
I'm not saying all of this one-sidedly. Even as I typed all that above, I was cringing.
One one hand, a person is being... well... what is normally considered a douchebag. On the other hand.... there's a plethora of issues with playing brand new champs in ranked. Heck, there's a plethora of issues with certain champs being present in certain games (hence the ban options). A champ doesn't have to be banned by riot to be selected in banning phase.
Frankly, I'm torn. I consider it unsportsmanlike and trollish to bring a champ into rank that you have little-to-no experience with, and in the case of new champs, that puts almost everyone into the "little-to-no experience" category. So on one hand, I consider banning a brand new champ to be pre-emptive team defense against all sorts of shenanigans.... much like with any of the 5 other bans.
On the other hand? Yeah, you're right. Normally it's a pretty low blow to ban someone that a teammate intends to play, whatever the reason. Not exactly the best way to start out on the right foot in most cases.
So I'm kinda torn on it. I've been on both sides. I've been glad that someone banned an intended champ in certain situations, and I've been pissed when someone banned mine.
I can see both sides of it.