Zinovia
Explorer
Are you referring to the races described in the Monster Manuals? If so, there's no need to ban them, because they're aren't intended for pcs, anyway. The stats are for npcs only.
Those yes, as well as minotaurs, which I believe received a writeup in Dragon. I don't want people playing kobolds, orcs, hobgoblins, bugbears, lizardmen, etc. etc. I don't see the MM character stat writeups on all of those as necessarily being solely for NPC's. They seem to be options that the DM might choose to allow for PC races if desired. I've seen those races used a fair amount on the character optimization forums over at the WotC site, generally for stat bonus synergies.
At the time we created characters, we had only the core 3 books to go on, along with the Forgotten Realms player's guide. I told the players they couldn't make a character of any race that didn't have a writeup in the PH or FRPG with the exception of gnomes, if they really wanted to play one. No one did.
Oh, I don't allow warforged either. They need to stay in Eberron where they fit in very well. No sentient robots in my fantasy world please. The restrictions were not done to limit player options so much as to preserve the flavor of that game world. I think that there are a good variety of options for them to choose from still, especially with the addition of the PH2 races.