I rarely write about dark stuff, for exactly the reasons you give - I don't need my brain going there. And I know I'm leaving a huge amount of money on the table as a result. But that's OK. I write here for me, and any money I make is a bonus. Medium itself didn't set a great example when they picked the grand prize winner of their writing competition - a long dark piece about suicide. I guess they know what you've noted here - dark topics sell.