My personal favorite is when coaches switch pitcher and catcher 
(OK being really sarcastic here - just for levity)....
People who are anti pitch count invariably bring up baseball history, but conveniently leave out that the game and hitters have changed a lot since then. Were Spahn, Sain, Marichal, Ruth, Young, Mathewson, etc. all pitching since they were 8-9 years old? Were they playing and pitching year round? Were they going into a travel league circuit to pitch games in front of college scouts who had their sundials to get their velo? Or did perhaps they actually grow into their bodies before seriously taking up pitching? (I'm too young to know - hahaha).
I get the whole pitch count argument and believe in it in general. It's a hard subject though because it is different based on development of a child as a pitcher. These are conversations you have to have regularly with your child. Before HS I think it's certainly the parents obligation to talk to whatever coach you have and determine their knowledge and acceptance of pitch counts. Also whether the coach has a love affair with the curve - yes a different rabbit hole we could jump into. Then make decisions whether you want to pay and play for that team. At HS - trust that your child will have taken all the conversations you've had and that he'll talk with the coach. If not, then there are ways to casually talk with the coach about his "pitching or pitcher" theories. Although I suspect most HS coaches come with a bit of history so you should know your answer beforehand. There are parents who decide not to have their child pitch for a specific HS and only go the showcase/travel ball option with a coach they do trust.
In the long run pitching isn't an inherently normal action for your shoulder as I think *any* parent has been told when they invariably take their child in for some sort of injury. Which all too often happens regardless of how you've protected your young pitchers with pitch counts, don't throw curves, eat your veggies, don't swim in the summer before the "big game", etc.
Those old-timers probably did start pitching young and may have pitched MORE than today's youth. However, I would caution against anyone using that to make the argument that the higher pitch counts actually BUILT durability (although I think there is a decent subargument or two that may have merit). I have a theory (and that's all it is since it wouldn't even be possible to find the data I would need to prove it). I think there are those who are genetically able to sustain heavy loads pitching-wise. They aren't as susceptible to arm injuries. In the past, before pitch counts were considered, I think those that were so genetically gifted, survived the gauntlet of youth ball and many got to the majors while many other pitchers "blew out their arms" and were left behind. Today, we pay a lot more attention to a pitchers workload and we baby (and I don't necessarily use the term in a bad way) young arms. So, a lot of hard throwers today make it as far as the pros before they start seeing problems. In the past, these same pitchers might have been done somewhere in their high school years and we'd never hear of them. I think we are seeing the first generation of pitchers who have been under pitch counts since they started. I think a modern focus on pitch counts has led to a lot of guys going farther in their careers.The result is a much deeper pool of hard-throwers.