Speaking as someone who runs quite a lot, I would be very interested in seeing you quantify this point and cite supporting research.
In particular, I am skeptical you can find a peer reviewed study which suggests there exists a causal link between running n miles per day and requiring hip replacements later in life. Likewise, what is the "optimal amount" of running you speak of? And for what purpose is that amount optimal?
To put it bluntly I think you're choosing the wrong activity for the "you can get addicted to anything" argument. I don't have an issue with that idea in the abstract, but I think you'll have a very difficult time mounting a persuasive argument using the idea that most serious runners are "pathological" - unless, of course, you presuppose the idea that doing things pathologically isn't unhealthy.
EDIT: Here is a study which directly contradicts your claim about excessive running and hip replacement[1]. The ~75,000 respondents under study demonstrated a reduced risk for osteoarthritis and hip replacement.
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