And they'd be wrong. Anyone with any amount of common sense will realize that a player sliding into you (even with spikes on) isn't nearly as dangerous as a guy hitting you like a middle linebacker would. The shortstop/second baseman also knows they can jump and avoid (for the most part) being taken out. The catcher is left in no man's land because he has to be within reasonable distance of the runner because of the tag. Nishioka could've just as easily touched and stepped behind (in relation to first base) second base and thrown to first.
I'd be willing to bet the ratio of catcher's hit/injured is a lot higher than the amount of middle infielders hit/injured.
Lastly, and this kind of builds upon my last post, if running over the catcher is "part of the game" why don't base stealers attempt to take out the middle infielder receiving the ball? Why is it limited only to the catcher? Posey did exactly as a second baseman would (attempt to field the ball in front of the base) and if it was a middle infielder that got run over, there's no doubt in my mind most people would say it was unnecessary and a bush league play.
Will you at least admit that If it wasn't for Posey's poor footing and dropping to his knees he wouldn't have gotten injured?? If he would've actually prepared for the hit like he was taught, then he would've gotten knocked backward onto his rear and the only thing hurt would be his ego.
Are charges necessary in basketball? What about fighting in hockey?
Finally I would like to bring up one last point. In the baseball rules (the actual rules, not the unwritten rules) when discussing blocking the path of the runner, it specifically states the following about catchers:
"The catcher, without the ball in his possession, has no right to block the pathway of the runner attempting to score. The base line belongs to the runner and the catcher should be there only when he is fielding a ball or when he already has the ball in his hand."
Posey Clearly throws himself towards the plate as Cousins is coming in. Cousin is assuming that Posey is going to block (and rightfully so based on the play of the catcher). Posey didn't get entirely into a blocking position in this case, but if the umps aren't going to call the game as the rules stipulate than Cousins has to assume that Posey is going to catch the ball and try to block the plate.
Unless you can convince the umps to actually call the game by the rules in place then you are wasting your breath. Was it a horrific accident...yes, but you didn't see any rules put in place about blind side hits that go over the top when Joe Thiesman broke his leg.
Our society is very reactionary, and unfortunately not proactive. It takes people getting tons of concussions for people to start caring about them and it take someone breaking a leg before anyone complains about plays at the plate.