Surely, you can "come out" only if you are
gay?
But seriously there is a case for
not writing under one's own name. Google is everywhere these days, and uses very clever methods to identify what is a person's name, and to link it to various sites. And any smart prospective employer will google on your name, and if he finds you are posting anti-business left wing views everywhere then you won't get the job.
Closer to home, it is not possible to write anything of value on a lot of aviation stuff e.g. maintenance practices, other than under a pseudonym, because the field is ridden with so much incompetence and even malpractice.
And the CAA reads these forums; that much is clear from the speed with which they have taken some things off their website after the URL appeared in the Pprune medical forum
I know of a semi-private forum where full names have recently been enforced and this coincided with a rapid drop in the contributions. To be fair, it did not help that one chap (an aviation business) joined up, didn't like some past postings, and threatened to sue some people, but if people used nicknames he might not have been able to do that. That incident taught people a lesson and I can see a lot of them dropped off after that.
Many years ago, Compuserve ran a load of forums where your full name had to match the one under which the account was billed. These forums were OK up to a point but were much less useful than anything subsequently on the internet.
Here, most regulars know each other, and many have met up, but nicknames keep the search engines from adding 2 and 2.