Users can always start a throwaway account, and post in a thread. That's done on reddit. It may be more difficult to start a discussion with a throwaway account, but I suppose it could be done. I just discussed this in the open thread. Some etiquette was covered:

• Indicate clearly, and from the beginning, that the account you're using is a throwaway. For example, "this is a throwaway account..."

• Use it to discuss topics you don't want to have your real name, or your regular account linked to, but don't use it as an excuse to engage Less Wrong at a lower level than you usually do.

• Don't use the throwaway account as a mask to get away with trolling, harassment, bad jokes, vitriol, or not trying to be reasonable.

The community may be indifferent, or sympathetic, but usually not exclusionary. I mean, if somebody is using a throwaway account to discuss why it's rational for all of us to start hating this one particular outgroup, that would deservedly receive flak. However, maybe someone wants to discuss really signing up for cryonics, but the feel it's still too weird to have their name publicly linked to it. Or, maybe, they have a problem they believe Less Wrong might be able to solve better than other online, or meatspace, support communities, but they're embarrassed for people to know it's them. If I was in that particular sort situation, I would make it clear that I'm already a regular user of Less Wrong, and it's too harrowing.

However, no user would be obliged to qualify why they're using a throwaway, even if another user doesn't have the perspective to understand why a throwaway might feel necessary.