I think most Black Mirror episodes have multiple moral tales to ponder. For this episode, your thought is certainly one thing to ponder. I also felt that it really spoke to the dangers of anonymous mob justice (or Anonymous/LULZSEC justice).
Yes, the characters were morally corrupt and reprehensible. But do they deserve to be tortured to the point that they were? Felony records, murder, and a permanent smearing of their name? Is it justifiable for a small group of people, who aren't accountable to anyone, to make decisions that destroy the lives of others?
I'm shocked at the sympathy towards a paedophile. He was eyeing up a child right at the beginning in the restaurant. He deserved everything.