You seem to be forgetting that a marathon is -a race-. Am I offended by any of those things? No, of course not. Would I be offended if those people claimed to be a competitive tennis player or swimmer or skier? Heck yes.
Think of it this way. Would you ever go up to a famous actor, heck, even an average actor, and tell them, "Hey, I act too! Well, sort of. One time, I watched one of your movies/plays, and then I repeated some of the lines to my wife later that night. It's about the same, right?"
I personally don't care what these 5 hour marathoners do with their time or money, and am not "offended" by what they do. But don't go and tell me that the difference between a 2:30-2:50 marathon and a 5+ hour marathoner is the same as the difference between 2:05-2:20 and 2:30-2:50 marathoners, because that simply isn't true. One is a difference in talent and resources, and the other is just flat out disrespect for what it takes to succeed at something difficult. Would you practice for climbing a mountain by going to your local park and crawling up some hills?
The marathon, like anything that requires a lot of patience, training, and dedication to complete properly, deserves respect. No one is saying ban them from the sport; all anyone is saying is give the marathon the respect it deserves, and treat it like any other race.