One of the highly touted benefits of the internet that has been praised since Godknowswhen was precisely that it was anonymous. That everyone had equal access to the information and an equal ability to provide information to others. Then, the receiving individual, now with access to more information than they had ever thought possible, was free to make up their own mind about what they want to do with the information and the onus came upon them to decide if it was true or not.
Of course, just as in other situations, knowing the identity (whether the “real” one or a brand name as it were) is helpful to determine whether or not the information is reliable (to use a SDMB example, someone would trust Quagdop more than Handy when asking for medical advice*). As such, having some measure of identification is helpful. If the SDMB were to assign a random username to the poster each time, things would get confusing and I doubt that anyone would continue posting.
Would people still continue to post on the SD if they knew that their ultimate identity were to be freely available? There have been threads on this before. I recall that one poster gave his full name and home town (of course, they could have been lying) and another poster said that they are scared to death that someone would find out what they’ve posted - like her mom logging on and reading some of the things she’s said.
Of course, many Dopers like to go meet other dopers and, over the course of time, have come to know their peers far better than just posting on the message board. One doper even recently had a party at her house (there have been other examples of dopers helping others move, etc.).
That doesn’t directly relate to your question, but perhaps it provides some information that will help you. As for your question, if the SDMB suddenly provided your “real” contact information, I think the boards would drop out of sight very quickly. If for no other reason than people generally don’t post their addresses on the internet in general (spamming and etc.). I think an equal number would probably drop out because they would suddenly be held accountable for their opinions and most of the debate would grind to a halt.
On one hand, I think that shows a lack of conviction in themselves, but I certainly wouldn’t want my personal information broadcast over the 'net, other than what I personally have posted in the past. To be fair, there are a number of posters who would continue to post but would become a bit more guarded in their messages and others who would continue to post as they had before.
*The advice-seeker should of course look to their own physician rather than internet message board posters, but you get the idea.