Masha Gessen, writing in The New Yorker:
I can think of only two explanations for why the Capitol Police failed to prepare appropriately or to respond forcefully. One is that they were in cahoots with the invaders. The other is that they did not take them seriously, which is to say, did not fear them. I will dismiss the first hypothesis because it’s a conspiracy theory. Evidence for the second hypothesis, however, is abundant, and it extends beyond the Capitol Police.
As Jamelle Bouie points out, it’s possible to be both ridiculous and deadly serious — look no further than the KKK.