Tony Stewart's broken leg has, once again, put the spotlight on the potential damage a driver can do to his championship hopes should he (or she) be injured while driving in other series.
As the team owner, Stewart doesn't have to answer to anyone about his extra-curricular driving; but, ultimately, his injury could cost his team a chance at winning a championship which is their ultimate goal.
Stewart has called racing sprint cars his "golf game". It's his chance to get away and relax. It's also something he really enjoys. If you take away these respites, is there a greater negative effect on the person than the risks of injury? I believe so.
Bottom line: these top-of-the-line race car drivers are risk takers. It's what gets their juices flowing. It's why they're successful on the track. They enjoy the adrenaline rush that comes with driving fast in tight spaces. It's in their DNA.
A few years ago, I read a book about the Original 7 astronauts. Most had been test pilots who put their lives on the line daily. In talking with their spouses about the daily possibility their husband may not come home, the author found that they understood the daredevil-like needs their husbands had; and, in fact, that was probably a part of their personality that attracted the wives to them in the first place.
Most Sprint Cup drivers are the same. If you forcibly take those adrenaline rush opportunities away from them, you stop them from being the guy who got here in the first place.