Water-man: That explanation is in the first page you hit when you try to sign up, put there over a year ago so that staff shouldn't have to repeat it in these kinds of threads.
http://thefiringline.com/privacy.html
We're not unreasonable. If there's a particularly compelling reason for a request, even though it
typically wouldn't be granted, contact staff privately and explain it.
Not being able to read the outline of privacy and data-permanence expectations that's put right in front of you when you sign up, alone, is not a very compelling reason for staff to do anything. And even without that page, there are certain obvious expectations about signing up for, and participating on, a forum. Expecting account deletion and post removal is, in general, not very reasonable.
Ask yourself this question: What interest do you have in account deletion or mass removal of posts that isn't outweighed by maintaining continuity of historical threads? The fewer posts you have, the less potential damage, but also the less reason to delete them.