Losing the reflecting ice will increase the average global warming rate. And you don't just melt an isolated piece of ice in the middle of the terrain, not to cause a change of a global trend at least. Melting enough ice means melting a lot of floating ice, than will not expose rocks but dark water that will absorb far more direct heat than the indirect heat trapped by the relatively small amount of captured CO2.

It is like saying that you should not be scared about falling from a cliff because the air resistance will lift you back up to safety.