I've had people 'pop' to venues I've run just to give out flyers many times in the past, and it didn't really bother me. They paid the entrance fee, and if they went home early then it was their loss. I did notice though, but just thought it a bit odd / cheeky, none were going to affect my event, so I had no reason to stop them doing it.
To 'defend the practise' though, I would fully understand someone refusing flyers that were of a 'rivals' night - When I say 'rivals' I mean someone unnecessarily putting on another night that has a direct effect on the event / future events in question. There's a lot of it about and a bit of standing up for one’s venue is understandable.
If it’s simply money orientated, I'm not impressed - If it's a genuine 'soul' sticking up for their event, then power to em.
All the best,
Len