I am old school and grew up with the idea that if you were "wronged" in baseball field you took care of it and that included hitting a batter. I have changed my mind as I get older. Simply not worth the risks of permanent injury. I,also, realized at some point that these are children playing and for an adult in charge (or for that matter not in charge) to hurt a child on purpose. is simply stupid. The learning point for me was when my 15 year old, at the time, talked about throwing at a batter because his teammate was "wronged" on the way home from a game. I said he shouldn't do that and he simply said "why not dad, you would have". Sometimes it takes our children to teach us by looking in the mirror what we have taught them.
As far as slashing, not a big fan but it is legal. Pitcher can help with that by throwing inside (not at the batter but definitely inside) or high, hard to get around on those pitches if he pulls back then swings. I guess it does depend on how hard the pitcher throws versus hitters bat speed.