most of these copy/pasters don't read the rules before they embark upon their career of stealing other people's words, and for another they probably don't see plagiarism as doing anything wrong.
Considering how many accounts were banned because of copy and pasting, it may be worth to add warning in the field of sending message.
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I suspect that most plagiarism spammers are run via automation, and the person behind the account will never see that warning.
I wouldn't say most, but obviously I have no facts to back this up. I think the case will likely be that most actually just do it manually, especially the smaller scale farmers who just come here to earn a little extra in their spare time. They probably have no idea about bots that do this or where to even get one so they'll either just find a post in a big thread and copy it, or sometimes they post it into a word-spinner and then post that to give them an extra layer or protection against detection. It's really simple and requires very little effort. Most are likely 'forced' to do this due to the fact that they can't speak English to an acceptable standard if at all. Then of course there will be the smarter users (or abusers) who will have bots that do this all for them, but I think they'll be amongst the minority (though they probably generate the most amount of spam given that it's automated). Hopefully merit will have thrown a huge spanner in the works of the bot abusers now but previously they will have been raking it in with ICO campaigns who would accept anyone and pay for anything with no quality checks.