[PragmaticPulp]

Basically, ignore any subject matter that tries to reduce cortisol to being "bad".

Cortisol isn't inherently good or bad. It's context-specific. It's not something you want to universally lower. In fact, if you take supplements or medicine that significantly lowers cortisol (e.g. by inhibiting cortisol synthesis) you'll find that you don't feel very good at all. You need an appropriate amount of cortisol to respond to activities.

Running extreme amounts (100s of miles per week over and over again) should be approached with additional education and appropriate attention to one's health, but generally speaking someone running for fun and paying attention to their body (e.g. don't force yourself to run if your body is telling you to take a break) doesn't need to worry about anything.