I don't agree.

IMO "griefer" has a pretty defined meaning and implies a player who is going out of their way to be a jerk and, well, cause grief.

I'll agree that "looter" could be understood to be a scavenger and not an inherently anti-social player.

So if you just said looter I'd agree with you. When you say griefer I don't - IMO a griefer is inherently a jerk (player, not character)