Okay so what do posters intend to do about it? Genuine question.
Oh, wow -- so we're actually allowed to have ideas? I thought even raising the subject of privacy protection, in any form whatsoever, was a pathetic pointless whinge?
Your posts say so much more about your own worldview than MN. If you assume that profiting from the site is the sole concern, to the extent that they have absolutely no interest how anything impacts members more readers, more traffic, more links: end of why don't they take money from payday loan adverts? Especially at Christmas: great time to catch parents who struggle to afford gifts for their kids! Why don't they run special offers on cosmetic surgery fix those saggy boobs and mum-tums, ladeez! or alternative 'cures' for autism, or MLM firms or anyone else offering a wodge of cash?
It's not inevitable that all content of a website is immediately, entirely and freely available for rebroadcast. I don't know the legal position but, as WhatsGoingOn pointed out, MN does claim copyright of posts. Whether lifting large amounts of text from threads to form the main body of an article used by a professional (ha) news outlet consitutes fair use, I don't know.
Practically speaking, there absolutely are measures that can be used to prevent easy skimming-off of material. Yes, everything here's public, but there are different degrees of that. It doesn't have to be so easy for others to wander through, picking out stories as it suits them.
I know another forum where certain topics are restricted access, and you have to log in to view them, and enter a password which is posted elsewhere on the site. In one of these topics, you can't even post unless you've accrued fifty posts elsewhere. None of these measures are insurmountable (and they're not designed to be), but they cut down on random browsing the rest of the site is heavily used and goady fuckery, and maintain a strong sense of community and responsibility between posters, and that seems to work pretty well.
(I'm rereading that and it sounds vaguely dodgy. It's just a writing site, where people need to post work-in-progress without it being nicked, trolled, spammed by fake agents or potentially losing first publication rights.)
I'm not saying that's right for MN. But there are options. We don't just have to throw up our hands and say of course this is open season for the Daily Mail.