When people say things like that to me, I agree with them. Marathons are a bit excessive. You can achieve most of the benefits of marathon training by running 30 minutes a day. Unless you have a passion for running and a desire to run the Marathon distance, there is no compelling reason to do so.
I'm in my 40s, so I can't speak for the youngsters, but Marathon training leaves me in a perpetual state of achyness, if not outright injured. I was at a wedding reception, and I was in fantastic shape at the time but hurt so much I couldn't dance. Something is not right about that.
It kind of reminds me of the old-timers who say "back then we didn't know how bad smoking was for you." I call BS. Ingesting hot smoke into your lungs and coughing up brown stuff all the time isn't a red flag? Use your brain!
Every time I run a Marathon I feel like I'm intentionally injuring myself. Common sense says that anything that takes you from the the top of your fitness and back to square one in a day can't be all that good for you. It takes me about a month to feel like I've fully recovered from a Marathon. Let's be clear, I'm not talking about the fools who walk the Marathon just to finish it. I'm talking about the fools, like me, who leave a trail of blood and sweat 26.2 miles long and barely hobble away from the finish line.
So why do I do it? Even though I feel that it's bad for me, I enjoy the process of training and building up, and I enjoy the flood of emotion that comes from cashing in all of that fitness all at once -- all my eggs in one basket. It is an amazing feeling, and the benefits do outweigh the drawbacks when all is said and done. Running IS good for you. My fitness has never been better than it has been when I am at the peak of a Marathon training cycle. One or two races a year that set me back a bit are not going to kill me, especially when weighed against the overall fitness gained from consistent training.
Still, I must admit that Marathons take a good thing a little too far.