Originally Posted by
Helden
They weren't just protecting people from the Lannister forces, they were protecting people from pretty much every army.
And even then, they were already taking from the people because they needed to eat, its only a short step from that to start taking more, and this is years after we last saw the Brotherhood, at this stage in the books they'd stopped helping people and were just hanging anyone that Lady Stoneheart was pissed off at. And she's pissed off at a lot of people.
I personally think that Beric died and actually stayed dead at some point, either because Thoros realised that Beric was becoming less and less himself everytime he came back, or because he finally got caught and someone chopped him into Beric nuggets so he couldn't come back, and after that they just became outlaws.