My experience with masks, and idk if other people have noticed/feel this way, is that many, many people think masks give them much more protection than they actually do. The problem occurs when this causes people to seem to care less about maintaining social distancing and whatnot. People are just generally less careful. In Region of Waterloo, for example, where I live, mandatory face covering while inside a public place came into effect July 13th. Since then, I have definitely noticed people being less cautious.
I recognize this is anecdotal, but I feel like masks are being oversold, with slogans like "save lives, wear a mask." I feel like that is dangerous wording because that's not what masks are capable of.
Bringing it back to baseball, this could also drop the guard of the players like it does with regular people. That's my worry.