Big tech social media for sure (especially the video platforms). Their algorithms are predatory as fuck.
Just the other day here there was a guy that killed his wife because she wanted a divorce, and his messages were stuff like “I am an alpha” and shit like that, mentioning stupid “influencers” and “coaches”. This is just one more idiot who was brainwashed by targeted content tailored to create echo chambers that breed extremism because it drives up engagement and ad revenue.