@D Wolf - The AI rarely uses Mercantilism if it has any alternative, and it makes no real allowance for corporations in its decisions. Since Free Market must be available by the corporation phase, most AIs will be running that (it's State Property that's the problem). If you've got a merchant, you might want to hang on to him unless you're confident of getting another (e.g. the free one from economics).
I'd also add to the list of points in favour of enviromentalism that you can force everyone into it with the UN, opening all markets to corporation spread. If many civs are staying in state property, you can actually come out ahead on cash. Dubiously, the AI loses money through extra corporation costs, but similar to mercantilism I don't consider doing equal damage to your civ and the AI a genuine benefit.