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Presumably, they're running. The goal, in a marathon, is to run whatever distance it is that one runs, as fast as one can. In what way is an amateur who has trained for the race and who runs from start to finish "wrecking the spirit" of the marathon? As long as the person is actually propelling himself or herself in a reasonable approximation of the running gait, and makes it through the whole race, what's wrong with that? Just because the person in question can't be a professional athlete or can't run it at a time of which the author of the article would approve (but can't do himself)?
This, by the way, is the attitude prevalent in Soviet Russia at the time I was growing up. If you didn't have the talent to make it to the Olympics, forget about learning any kind of sport, or music, or dance, or anything like that. Nonprofessionals just didn't do these things. (this seems to be the world that the author of the article yearns for...)
Was it really "better" than the US, where enthusiastic amateurs participate in just about anything? I'm not sure. When I was a child, my mother wanted to enroll me in a gymnastics class, just to get me off the couch and to get me more physically fit. No class would take me for any kind of money; I didn't have the talent to make it to the Olympics, and they didn't want to waste their time on an amateur. So, I stayed on the couch. I didn't start participating in regular physical activity that I enjoyed (school PE did not count because I really did not enjoy it) until I was 24 and living in the US.
Note that under those standards, the author of the article would not be allowed to run the marathon any more than Oprah (or any other amateur) - his time wasn't all that much better than hers. The only people allowed to run the marathon would be the elite Kenyans and elite Americans who train full-time. And we would all be resting our fat butts on the bleachers and watching from the sidelines.