Isn't that when trolls decided to post child abuse material on lemmy world? Since it's a large instance it federated to a bunch of others whose admin, rightfully so, decided to take down their instance to avoid legal repercussions, as well as take the time to clean everything up
They get hated on because :
they inspect packets. They terminate the TLS sessions at their servers and reencrypt to forward to the backend. This allows them to analyze the data to spot spam, optimize compression and such
they are used everywhere. If they go down, 30% of the internet goes with them.