Too much exercise is a problem that can happen to literally anyone. Not just due to injuries. Fatigue management is one main component.
Saying that more exercise is always better is a completely false statement. Do not care if it sounds good or is meant to "help" people or whatever, it's completely false and can harm uninformed people.
This guy looked at longevity stats for runners. He recommends running a little, not a lot.
2012 TEDx Talk: https://www.youtube.com/watch?v=Y6U728AZnV0