I'm not a pro pilot either, but grass is more likely to cause the aircraft to flip, due to its relatively irregular surface, and even if no flipping occurs, will likely cause more damage, for the same reason.
I've landed on the grass at NZWB, and it feels pretty darned good, one of the better grass runways, but the suspension soaks up a lot of the bumps. Also, despite appearances to the contrary, grass can be almost as hard (unyielding) as seal to land on. Hard+ bumpy = broken aeroplane.