It really peeves me to see people walking towards the end of 10k`s and half marathons so I say ban them!!! If you ran in a walking races you`d be warned and then disqualified so why not the same in our events!??!
(It is especially annoying to find out that you`ve persevered with running only to hear that you`ve finished behind others whose race plan seems to be a mixture of fartlek and intervals!). At least I keep on running, albeit slowly!