Give me a good argument against having 6CBs in our squad.
The fact Song was purchased a year ago or that Mascherano, however much I like him, is Argentinian is not a compelling argument. A fifth CB is not that stupid since Puyol is injured half the time, but a sixth just does not make sense. Especially if we want to give some time to Bartra. If you don't want the latter, just sell him now. He won't develop himself by sitting on the bench or watching from the stands.
EDIT: Let's make it clear I am not trying to belittle your idea of Mascherano, I just don't see any argument for starting with so many CBs. I'd love for Vertonghen to come and another, tough and tall CB. But then either Song or Mascherano has to go...
I just think you're over thinking it, mate and panicking over a situation that most will welcome. We've had problems at CB as you know and providing plenty of cover means that it is unlikely to be a problem in the future.
I'm not saying being a certain nationality is enough of an arguement, but with Mascherano being the same nationality as our new coach, there will be an obvious understanding between them and if i'm not mistaken, Tata has already stated he will be counting on Mascherano, someone who he clearly has a lot of respect for as a player and person. So that really says it all (and it's besides the point anyway, because Monster Masch is a boss).
As for Song, he was bought for similar reasons to the aquisition of Mascherano. Although not as good, he's still a great squad player and able to fill in at 2 or 3 positions offering strength and energy when needed. That's the logic behind these two specifically, they're not regarded as CB's, but as utility players, able to account for more than one position and help in reduce the overall number of squad players for the season.
Of course we'll have to wait and see what Tata and management have in mind for the CB position and although I agree that it could potentially result in overkill, unnecassary purchases that are ultimately unfair on certain members of the team, it won't be the worst situation.
One last point - Bartra isn't good enough or making speedy enough progress to break in to the starting line-up when everyone is fit. He reminds me of many promising Barca youth players, obviously good enough to be considered for the first team, but requires competitive football to improve and is too weak to make the impact required.