According to the Oxford Dictionary, "Plagiarism is the practice of taking someone else's work or ideas and passing them off as one's own"
Plagiarism definition in the forum is not the same as in academic space. The definition on plagiarism can be universal or local and you can see Bitcoin forum is a strictest forum against plagiarism in comparison with other cryptocurrency forums.
It is case to case basis, and with my experience here, it's time to time basis too. What is time to time basis?
Punishment on plagiarism can be different at different times, sometimes it was nothing (forum did not care about it), sometimes it was strict, sometimes there is second chance but strict reviews, sometimes second of second chances, and sometimes a poster must make dozens of plagiarized posts to be banned.
In general, I'm all for being lenient. There are users who have been temp banned many times but still haven't been permabanned because their contributions outweigh their misbehavior. I
actively disbelieve in the idea of a "rule of law" where hard rules exist and are strictly applied across the board as if we're all robots. Every case should be considered individually in the context of the forum's mission.
Plagiarism is what gets people permabanned, not just copying. Plagiarism is copying with the intent of passing the work off as your own. In essentially all cases, plagiarism deserves a permaban because it usually proves definitively that the person is here for the wrong reasons: to fill up space in order to get paid, not to actually discuss or contribute. If someone was able to convince us that they were plagiarizing just to eg.
impress people rather than to fill up space, then a lesser ban of a few months might instead be warranted. But this has never happened AFAICR. (Arguments based on plausible deniability aren't going to work; we don't need to
prove that you had the motive we see in your actions.)
If you treat posting as a job, a chore, then you must live in fear, since the forum is not made for you. In this case, you need to blend in as someone who actually cares, but plagiarism will immediately out you, and producing a mountain of useless posts will also eventually be noticed, if more slowly. If you do actually care, then this will be obvious in your posts (and probably your merit score), and you will have nothing to fear from moderators; even allegations of plagiarism will be doubted when seen in the context of your other posts.
in extreme cases could be copyright theft?
Plagiarism is almost always a copyright violation which could conceivably get the poster in a lot of trouble, but it's not a bigger legal issue
for the forum than anything else. (Using the forum to violate copyright is never allowed, though.)
when copying and pasting from the net can it lower google rankings? and internal copy and past could do the same thing?
That's not a particular concern of mine.
even memes may soon constitute copyright theft
Only in the EUSSR.