Well, there are six billion people out there, some of them must share the same name, surely. I know someone that used her real name as a poet, only to discover there's a more famous poet who shares her name

I haven't read all of this thread - and so I suspect it's been said already. But I've read some, especially the beginning.
Copying and claiming credit where it isn't due, is bad. Plagiarism in that sense is bad. But it seems to me, that you've realised plagerism is bad, very bad. And then just gone and looked it up, only to realise it's more broad than you thought it was. And then because plagiarism is bad, you've immediately condemned the new bits.
(That may not be the actual version of events, but you can appreciate the 'arbitrary condemnation' part of it)
Stealing specific ideas is bad, but like sam said with clancy, calls of "plagiarism" can go to far. Some people seem to take plagiarism far too far. And, unintentional plagiarists aren't bad people, it was unintentional after all.
This may have been dealt with on page 4, but I didn't read it.