This is my thought. For most of us, any exercise is more than what we're actually getting, and the best form is the one you're likely to keep doing. Even people who look unhealthy may be healthier than if they didn't exercise.

My main source of exercise, for 40+ years, has been cycling. Therefore I have very little upper body strength. This may be a liability when I get older and start losing that strength, increasing the chances of injury.

I personally think that young people should do some strength work in addition to the easy and fun aerobic activities like walking and cycling. The dangers of over training are their own beast, but not a worry for most people.