For those that don't know what any of that means (like me 5 minutes ago):
Arbitration is an alternative to going to court. Instead of suing each other in front of a judge, both parties agree to have a neutral third party (an arbitrator) settle disputes privately. It's usually faster and cheaper than traditional litigation.
The class action waiver means you give up the right to join with other users in a class action lawsuit against Zed. So if many users had the same grievance, they couldn't band together, each person would have to resolve their dispute individually.
Why tf are they afraid of being sued or class actioned against?
I haven't really used zed much and I'll delete my account and uninstall, just to show them that this sucks.