It could be considered filestealing if when userA grabs a file from UserB and then UserB don't longer have the file. But since UserB still has a copy then guess what it is called filesharing.
Not every torrent site out there wants to be a huge site like TL or some of the others and so they have never had the need to open signups and slowly but surely the site grows.
Like I have said before different sites have different goals in mind.
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