Pitchers need to give their head a shake. EVERYONE has to compete for playing time. The fact that the coach wants your son to pitch means that they better start working harder.
I thought you were going to go in another direction with this. My son has been asked to pitch in the recent past, and he has found that his arm simply isn't ready. He throws hard, and he gets really sore. He has had teammates in the past who have been in the same situation and have ended up hurting their arm enough that it then affected their ability to be a position player. What was OK at 14-15 yo is not OK at 20-22 yo.
YMMV.