He is doing it so he get's more gnw packs, 10 people do GNW = everyone get's a pack and easier plunder too i guess. As for should you stay in it, that's up to you and what type of group you want. I wouldn't, i like being in group with 100 active people, plus he is only motivated by greed and he makes your chances of going to cross server to meet other servers top groups low by having low power.