Isn't that so often the way? If someone isn't doing something just the way that we would then it isn't right, not valid, has to be changed or stopped. I wish I could say that I was immune to this but I'm probably one of the worst about wanting things done "just so" in accordance with my ideas of perfection. Here, Jesus reminds us that our way is not the only way.
Our Lord warns the Apostles, and through them all Christians, against exclusivism in the apostolate -- the notion that "good is not good unless I am the one who does it." We must assimilate this teaching of Christ's: good is good, even if it is not I who do it.