Long bouts of endurance exercise can be very taxing and destructive to many body parts.
Exercise as a whole can be done efficiently and effectively without wearing your body out.
Anaerobic exercise (lifting weights) can improve collagen and muscle production via several hormonal pathways. These same pathways tend to have negative feedbacks from excess aerobic exercise (i.e. high cortisol, low GH output in distance athletes).
The data on intense weight-lifting on the other hand is much more conclusive. Heart enargement, aortic dissection and a host of other heart related risks are sharply higher for extreme weightlifters.
Lifting a couple of days a week and doing cardio 3-4 days a week and not going completely nuts with either is probably the safest. But sometimes it's fun to go nuts and shoot for a goal. In the big scheme of things, there are a lot worse hobbies to have.
Again with the extremes; people don't get "big" on accident, and moderate strength training provides a whole host of benefits without the dangers. More people should be lifting, with proper form and modest goals.
How much of that is due to exercise regimes, and how much is due to PEDs? Steroid use is rampant even among semi-serious lifters, and not many people on drugs admit to it.