The key, of course, is balance. There needs to be a balance between discussing things of general, common interest, while at the same time maintaining some kind of integrity of the forums. Forums thrive on content, and when the driving force (Star Wars LEGO) is such a small niche, some allowances have to be made. If we ONLY talked about SW LEGO, we'd be gnawing the bones of old conversations within a fortnight, and FBTB would die.
So while HALO threads are inevitable, and perhaps even necessary, exercising restraint in the creation and use of such threads is vital, both for the overall health of the forum and for the sanity of the Mods/Admins. I gather that if there is restraint and sobriety in the usage of such threads, they'll be tolerated. N'est-ce pas?