Stephen Law on his new book, Believing Bullshit:
Intellectual black holes are belief systems that draw people in and hold them captive so they become willing slaves of claptrap. Belief in homeopathy, psychic powers, alien abductions - these are examples of intellectual black holes. As you approach them, you need to be on your guard because if you get sucked in, it can be extremely difficult to think your way clear again.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
(I plan to make these threads from now on. Downvote if you disapprove. If I miss one, feel free to do it yourself.)