Yeah, I am opposed to that actually. I can well see a scenario where Mertesacker will be one of the players in the first XI we want to upgrade in a year or two, and for that reason I think giving him the armband now is unwise; we may end up with a situation just like the one we are currently in with Vermaelen, and that is far from ideal IMO.
The perfect solution for me would be to keep Vermaelen another year and continue with the current situation, and then give the armband to Ramsey. We really should aim to get a long term solution to this, and Ramsey looks the best candidate to me. He is not very vocal, but he leads through example. We still will need vocal leaders like Arteta and Mertesacker though.