Although it is known that concussions cause lasting harms, those harms aren't always noticeable. Our brains have a limited capacity to repair themselves, and that capacity is slowly expended when it's used, which is one of the reasons why people who have had many concussions (playing youth sports, for example) are more likely to have detectable neurological damage in old age. There's less reserve capacity and thus more vulnerability.

I can easily imagine a person who decides that the loss of some of this reserve capacity is worth gaining the insight into what it's like to be in a concussion-induced altered state of consciousness. I don't say I understand or empathize with that decision, but that isn't the point.