The idea of people helping eachother and waiting on a mob and even resetting it so more people can gain access to the fun and endgame stuff is far more reasonable and noble than this pull early its your mob go for it mentality thats promoted here.
I'm not saying you should wait 5 minutes on a mob but if you know people are running there is no need to be selfish give it another 30 seconds someone else might do the same for you another day.