The fork has nothing to do with money supply, it has to do with whether and how to relax a constraint on transaction velocity before that constraint becomes a limiting factor of Bitcoin's utility. This fork is not inflationary or deflationary.
The fork is exactly about money supply. The primary argument used by those in favor of Gavin's proposal is that the fork is needed in order to make bitcoin more inclusive. If we make concessions to these demands now, what is stopping the same people from insisting we create 5 million bitcoin to airdrop into the wallets of some 3rd world country? When getting "mass adoption" is the primary focus, you end up with things like the dollar. I don't want mass adoption; I want sound money.