I was surprised as heck when my younger son announced out of the blue last Spring (sophomore year) that he wanted to play football. And I'd be lying if I said I didn't have some concerns, especially since, unlike most of the kids, he had never played organized fb at any level. But after checking out as many factors as I could, (coaching, medical support team, etc) I decided to let him go for it. He dove right in, worked his tail off in Spring practices, fought through some early training-related injuries, learned the playbook inside and out, and went from basically knowing nothing to becoming an impact player at OLB by the end of the season, and helping his team make the CIF playoffs for the first time in five years.
There is still a level of worry about concussions, etc., but my angst about some possible low-probability freak accident was offset to a degree by seeing the joy on his face in those special moments, like when the announcer called his name on three consecutive plays (tackle, TFL, PBU) and when they found out they were playoff-bound. Life is all about managing risk, and IMHO everyone has to make their own best decisions for their family.