Having played both highschool and in college I too had mixed feelings. I did more research and ultimately left it up to my kid. I never suffered a concussion in football and the only time I ever had my "bell rung" were on stuff that was easily avoidable and is now being avoided by better education and technique - special teams (full speed spear block that now would be illegal) and what we called blood and guts in high school where 2 guys line up and go at each other from 10 yards out full speed so imagine the bell ringing when an all state linebacker (the guy that rung my bell) and a d-end going full speed at this distance both dropping their heads, it was an accident waiting to happen and both of are "bells were rung". Coaches (good ones anyway) aren't doing these things anymore. I think it is about trusting the coaches.
Hence, my son now in 3rd grade and was fully educated about the risks and he decided at the last minute after leaning against it for a while that he was going to play so I signed up to coach too. I didn't encourage him, in fact fully supported him not playing as I thought that is what he was going to do. As a fourth generation college football player I was perfectly content having football as a family legacy die with me. And while I am not particularly worried at this age I wanted to make sure good technique was taught so why I signed up to coach and that experience has made me much more confident my son made the right decision.
We went to an 8 hour multi-day training on head injury prevention techniques and strategies and how to spot undetected mild concussions etc. It was really good and the game is soooo much safer for kids today. This son is always playing 2 sports and frankly I am more concerned now about baseball and soccer at this age. Being full speed in soccer with bigger age and weight distribution head to head contacts are sometimes really bad, in baseball they are getting to the age where they are developing throwing speed without great control or attention span. While I think in High School football clearly surpasses these sports in risk I think with proper mitigation the risks of any of these sports are outweighed by the emotional, and physical benefits of playing sports. 2 years ago, I said I wouldn't let my son play but I took the time to really look into it and I have changed my opinion.
Also it's worth mentioning, I never suffered a diagnosed concussion playing football through college (and if I had an undiagnosed one it would have been very minor) but had a major concussion in which I lost conciousness playing dodgeball in 4th grade recess. Obviously this is anecdotal but illustrates that all sports pose some risk and to be safe we need to do what we can to mitigate those risks and then determine if the gains outweigh the risks.