It's not fully general; it's an instance of a general argument that things are unlikely to be optimal in the absence of strong optimization pressures. Which is true.
Of course, that doesn't mean you should fine-tune humour; we'd need to look at the costs and benefits of doing that versus whatever else we could be doing.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.