I don't think Plagiarism is something that needs to be pointed out as being something you can't do. First of all, this is something that people should know they shouldn't do, for a number of reasons, and I believe most people who do this know it is wrong, but do it anyway.
Well it shouldn't have to be but it really does need to be pointed out that this isn't acceptable and you can see that from the number of threads from people in Meta asking why they were banned and if they can get a second chance, so people should be made aware of the rules and the punishments for doing this so there's no excuses then.
Also, I don't think it is as big of a problem in terms in the number of people getting into trouble doing this. Sure there are very many instances of this happening, however I suspect this is done by a fairly small number of people with a very large number of sockpuppet accounts, and I suspect this is often done via some kind of automation/AI.
Sadly I think you're very wrong. Copy and pasting and plagiarism is a huge problem and I'd say this sort of abuse is actually becoming endemic and almost commonplace now. Probably 50+ users a day are being banned for it and many multiples more will be getting away with it. Sure, there will be some times where a few individuals will be responsible for having hundreds if not thousands of accounts botting away, but there also seems to be hundreds of individual 'lone wolves' doing it as well with however many alts they have. I don't know whether there's some website that just suggests people come here and copy and paste posts if they can't speak English very well or people are just telling their friends and family to do so or they're even just actually figuring out how to easily abuse the forum by themselves, but it's mind-blowing how many people are doing it and it's sad to know that the admins don't look into any of it. I'm sure it's only the tip of the shitberg that even I know about and I dread to think of how many people are actually getting away with this on an industrial scale. Banning a few accounts for it when they could have hundreds or even thousands more going behinds the scenes is almost pointless and losing a few accounts a day will probably just become an occupational hazard to farmers. The only change that has been made is that they now require one merit or purchase a Copper Membership but when some of the worst offenders are making tens to hundreds of thousands of dollars from abusing bounties and campaigns they'll just purchase the merit or rank to bypass this. Merits can then easily and quickly be distributed between their alts and that's why I think we should require much more merit before you can start earning here, or at least make them buy a much more expensive Silver or Gold rank.