A large number of people post a large number of stupid comments on Facebook and other websites. When it comes to scientific discussions, the majority of people who end up “contributing” generally get their information dead wrong.
This is easily avoided by asking those people to learn about the material first. It’s too bad that they generally care just enough to post their bullshit, but not enough to actually know what the fuck they’re talking about.
But for those that do care, MIT has a wonderfully large set of online course material covering vast chunks of educational fields. I love the list in their physics department and I will be using it when some asshole brings up free energy again: