Pull Your head outta your butt wrote:
Once you enter a road race someone has started processing your paperwork $$$. They then order your t-shirt $$$. They even base their t-shirt purshase on how many runners are pre registered. Most of your entry fee is already spent before you show up on race day. We pay for the finish line crew based on entries rather than finishers.
Actually, many races in these parts don't give you a shirt if you aren't entered by a certain date or aren't one of the first 500 or 1,000 or whatever runners to enter. And if you pay for a finish line crew anticipating say 5,000 finishers because that's how many pre-entrants you have, and if 80 of those pre-entrants don't show up, but 80 bandits do, then you've got the same number of finishers, though any "good" bandit will bail out before going through the shoot rather than mess up the scoring system.
You have to pay for traffic control and permits one way or the other. Another dozen or two unregistered runners isn't going to affect the number of cops you need to pay and if it does, you've got "extra" money from the non-running pre-entrants whose t-shirts you can sell to spectators, runners wanting extra, etc to cover it.
So hypothetically, I'm running along my regular route on a summer Friday evening and hear footsteps behind me. It turns out that it's the Maude's Funeral Home and Brothel 8km which is held on my usual course on this particular night. So I pick up the pace a bit and run along with the crowd. I'm not supposed to run that night because someone put a race on my course?
If you ever watch Chicago Cubs baseball games, you've seen that there are houses in back of Wrigley Field that allow residents to watch the game for free. I'm sure the Cubs would rather that these dozen or so people buy tickets to watch the game, but there are some things a general manager or race director can't control.
The argument against bandits is that they have not really raced and any performance they turn in can never be verified officially. In the early 70s, there was a guy called Leo Duarte who ran a 2:15 marathon at a very low key race in Massachusetts that he hadn't entered officially. If you look at all-time US marathon lists, Leo Duarte is never there with his 2:15. That's the argument against banditing.