I'd say its horses for courses. Competitive serious runners particpating in club standard races obviously shouldn't. I'd say in Fell, trial, or off road races you probably shouldn't on safety grounds (just try overtaking someone on a narrow track and you'll see what I mean).
Anyone who's just tooling along at the rump end of a 10K or half thats traffic free - well where's the harm??
Personally I wouldn't - but I don't see the harm.
As to marshalls - well most of them are volunteers, usually from the organising club. Like referees at amatuer football games they do it for the love of the sport. I'm sure they don't mean to be officious. Maybe, on this occasion, like the rest of us do sometimes, they were having a bad day.