Yes giving a kid who you think isn't good enough yet to play at first team level 20 minutes in a match, even one your winning comfortably, isn't the brightest of ideas. I realise that a lot of people think that players are in fact robots with no human feelings, but they are very human. The younger they are the more human they are and the more likely they are to be negatively effected by a poor 20 minute showing in a game that's already won. Makes far more sense as I say to give them that little taste without exposing them to something which could end up being counterproductive to their long term development.
I'm not sure why you find this such an incredulous point of view. Especially when it's clearly the point of view of the professionals who are actually charged with making these decisions, and the owners who employ the people who they believe will make decisions based on what is best for both the well being of a single player and also the well being of the team as a whole.