Here is a reason (in fact, its my main reason), why I decided to become aan anonymous user:
I don't want every single one of my words on this forum to be archived for the rest of my life. This does not mean that I am saying things here that I would not say under my real name. It simply means that I don't want everybody to be able to google all these words in 5 years, in 10 years and even in 20 years.
In the same way, I would not like to have a transcript of every research conversation at work be printed and put on the black board of my university for the next 10 years. I simply don't like the idea of everybody (no matter who) being able to find all the stuff on the web that I said many years ago.
If the rules of the site would change in a way that they would require me to give up anonymity, I would simply stop using the site.