[dgordon]

No, "lots of people" don't kill themselves with marathons. A few people who try to go from couch potato to marathon in 12 weeks or who chug ridiculous amounts of water over the course of a 5-hour walk-jog kill themselves with marathons. (It's possible to drink to the point of excessive dilution of the sodium in your bloodstream, which can kill you just like dehydration can, but this is basically impossible to induce below an Ironman triathlon distance if you're reasonable about water intake.) That's not "lots."

Distance running is what humans evolved to do, according to a good deal of evidence. Admittedly, running on asphalt and concrete with awful form created by a lifetime walking and running in awkwardly built shoes and sitting in chairs all day is not what humans evolved to do.