If you're looking at this from an idealistic point of view then yes, Mark Cuban is  making a mistake backing ICOs.

But looking at this as a businessman, at a time when people are crazily throwing money at ICOs - he's very smart. Yeah, whatever ICO he backs might disappear in 3-4 years time .. by that time - Mark Cuban probably would've profited already and won't care - he'll probably be in some other business earning more money.

This was how he got rich, getting a business for low and selling it high.