Part of the issue is that what people precise as "crank" is heavily influenced by what's popular.

Kant had some actually useful ethical insights, but said some downright stupid things in the application of his ideas (like: You shouldn't lie to a murderer who comes knocking at your door looking for a victim, but you should "be silent" or something).

When I was first learning Kant I also thought this was stupid. But now after thinking about it a lot more I can see how this makes sense from a game theoretic point of view. If you model the murder as a rational agent with a different utility function, lying isn't a Nash equilibrium, being silent is.