I don't think it is possible for mankind to have too much faith. Even Jesus' disciples, after witnessing his miracles first-hand (healing the sick, curing the deformed, expelling demons, bringing the dead back to life, walking on water, calming the wind and waves, feeding tens of thousands with nothing more than a few fish and bread, commanding plants to wither and die) couldn't be accused of having too much faith. In fact, they had too little faith. Even after Jesus gave them the power to heal they couldn't do it in every instance.