Here's an update to the original post...
I met with the coach regarding the matter. We had a professional and cordial conversation. He said he was wrong about the decision he was about to make and he knows better. It was the heat of the moment and he lost his cool a bit. It was an awkward situation for all of us actually. I'm grateful for the conversation as I now have confidence that my kid won't be prodded to head out in a bad situation.
I appreciate many of the comments made here. What I find interesting is the fine lines which exist between the parent/coach/player relationship. To the coaches out there...The parent has final say over their kids health and associated risks. Not you and not the player. You have ZERO final decision authority when it comes to that. I would hope you're smart enough to look at a kids future and not your win/loss column when you are confronted with the preliminary decision or are acting on the players' behalf. Also, I think the "man up" comments demonstrate a naivety on the part of so many. I'm glad my son is competitive and doesn't want to take himself out of a game. Too many kids get used to "being careful" and lose their competitive edge. That one is on the parent. It gets to the point where they don't pitch if the humidity isn't perfect.
In my instance, the situation was so obvious.