Because you have to be pretty mad cuz bad to spam invites

This group is for all those no-lifers who invite you to one-member, no-avatar Steam groups that he made because he's a parasite spamming Steam with his worthless groups.

This group can have two meanings: 1) the person spamming you invites is bad because he spammed you with invites, or 2) by lowering yourself to his level, you are also admitting that you are bad (but his groups most likely already told you that you are bad), so you are, in essence, agreeing with him while reversaling his logic and forcing him into self-admittance that he himself is bad.