The rules for Current Affairs were laid down a while ago.
Current Affairs is primarily for the serious discussion of military-political topics and other matters which may affect us as members of the armed forces.
It isn't for:
1. Political point scoring
2. Attempts at comedy (which doesn't mean you can't be witty)
3. Propagation of conspiracy theories
4. Outrage threads
5. Baiting of cultural, ethnic, religious or sexual groups.
6. Threads centred on Race.
As to why the BLM thread was taken down.
It was riddled with racist abuse.
Firstly, to answer your question regarding the site being representative of our society, I do not believe that to be the case. This site is heavily military leaning, and anonomous, our society is not.
Secondly. Society in general are accountable for their actions under law. One two, or half a dozen people start being racisct in the General Populace then these individuals are easily identified and can be brought to justice. On this site it is not that easy. That said, The moderators are not here to hide racists but we are here to take down racist posts and dole out infractions in an attempt to stop them repeating. This is not a Town Hall meeting where neer-do-wells can be evicted never to return, nor is it a debating Society.
Members here are asked to stick to some (pretty simple) rules, however, those members that constantly infringe those rules will be removed from the site. The trouble is, they reappear quite quickly in another guise and continue in the same vein. In General Society, when one is punished, that individual does not have the opportunity to immediately pop up as somebody else and continue to break the rules. That is a fundemental difference between this site and and our Society.
The threads (or posts) that 'cross the line of law' as you put it, how would you like to make it possible to prosecute? Would you like the Site owners to dig out the miscreants personal details (the little they have) and hand it over to the law? Or, as happens now (and with tens of thousands other forums across the internet) the moderators take down the offending thread (or post) and that's the end of the matter? Threads are taken down to protect the owners of the site, It's their site, that they are responsible for, they merely lend it to us, (well it's free of charge) the Police have already spoken to the Site owners on another matter, none of us want that to happen again.
To finish, this is an anonymous forum with a scattering of keyboard warriers, a sprinkle of internet hard men trying to be edgy and a massive amount of excellent, hugely informative threads posted by informed and often very amusing members. Let the moderators deal with the minority trying to spoil the site.
Enjoy the site for what it is and because of it's very nature, expect to have theads pulled from time to time.