As to the evil which results from a censorship, it is impossible to measure it, for it is impossible to tell where it ends.
Huh. Whether by accident or talent (probably the former, since my computer skills suck), I've found a list of the biggest groups on bungie.net. To do it, use a blank space in the group tool, priortize member count, then check descending order.
Top 30 Groups:
1. The Spartan I Project (10,942 members)
2. Forgeworld (8,350 members)
3. Coup D Bungie (6,371 members)
4. Lower the Guns (4,259 members)
5. Atlas (4,190 members)
6. The Bungie Podcast (3,795 members)
7. Reach Secrets (3,756 members)
8. Reach Stats API (3,488 members)
9. Mjolnir Battle Tactics (3,291 members)
10. Owners of the Katana (3,217 members)
11. Waaahmbulance (3,034 members)
12. Forge Cafe (3,011 members)
13. The Marty Army (2,825 members)
14. Black Water Ops (2,820 members)
15. CompoundIntelligence (2,640 members)
16. Halo 3 Academy (2,270 members)
17. Foto (2,008 members)
18. Major League Driving (1,942 members)
19. HaloTrackas (1,907 members)
20. Epic Pic (1,864 members)
21. Forever Forgers (1,804 members)
22. Robot Factory (1,732 members)
23. Facility B5D (1,707 members)
24. ODST Recon (1,574 members)
25. BUNGLE (1,549 members)
26. Coup D Bungie 5 (1,420 members)
27. Sapphire (1,384 members)
28. The Black Chapter (1,335 members)
29. Death by Mongoose (1,219 members)
30. ODST 4th Battalion (1,199 members)
If memory serves, bungie long ago kept tabs on which group was what rank, but eventually abandonded the idea after a site overhaul.
Now for the facts. #1 Combined, these groups have 88,083 members. (Note many of them have been counted more than once.) #2 As of July 27, there are 19,487 groups on bungie.net. #3 This means 4.55% of all groups ever created still exist.