The bad thing about them is if you use Mo' Creatures and try fighting the short hostiles or the spiders in vanilla, and there is grass between you and the monster, you'd frequently hit the grass, and, yeah, grass actually decreases your weapon's durability. (Yes, I know it's because it counts as a type of block, but still.)
Same thing if you tend to miss your swing, you'll hit the grass. And with the crap hitboxes and the fact that you're playing in multiplayer, maybe this is worse, depending on your ping.
If only grass didn't damage your sword... (because it makes no sense, even if you hit dirt, sand, or even stone, the durability doesn't decrease unless you hit it for long enough. So grass dulls your sword faster than rock, and at the same speed as striking through flesh, wat?)
Grass is a part of the game, the terrain affects the combat.
I think grass should damage your sword, it makes sense that if you swing it, and it cuts grass, it will get duller as swords usually do.
It should be the other way around, it doesn't make sense that the sword doesn't dull when striking (but not breaking) stone, rock, and other blocks.