i'm not against the concept of rehabilitative justice
Rehabilitative justice is for civilians. Cadre discipline is completely different. It's no contradiction to think that civilian handling should be rehabilitative while cadre handling should be punitive. Cadre who fuck up should be made an example of and quickly expelled from the party. A social club is free to expel and bar prospective members from (re)joining their club, so why shouldn't it be any different for a party?