Most people use the service for perfectly legitimate purposes. On the fringes, however, some users abuse the software to share pirate libraries publicly, a considerable thorn in the side for rightsholders.

I’ve been using it for over a decade and I don’t know single person that uses it for “perfectly legitimate purposes” (assuming they mean "not for pirated content, considering the next sentence). There’s no reason to use Plex as a front end for all other streaming services.