I have seen/heard 3 umpires say this on 3 different occasions and it never caused one bit of drama/controversy. None.
It was refreshing to witness the transparency. Coaches appreciated it. Parents appreciated it. Maybe you should rethink your position. Times have changed. People appreciate transparency more today than ever.
You actually make my point for me on why you don't do these sorts of things. And why 'preventative umpiring' is taught heavily across multiple sports - certainly most I have been involved in.
On these 3 occasions, nothing happened. Great. And as an official, you probably are going to get away with it the vast majority of the time without issue. That is not the point.
But it well known amongst umpires that this action has the --potential-- of causing an issue and there is a lot of known reports of it causing an issue. So why put yourself in that position at all when you didn't need to? I can just as easily call a good strike zone without making any comment. Avoid the trap - proactively prevent a potential source of a problem.
There are many, many situations like this - excessive talking pre-game to coaches you know, or friends in the crowd are another good example. It can turn quickly - so do it properly and avoid the situation altogether.
There is a temptation as an umpire to try to find ways to get the crowd on your side or be friends with everyone or find "an easy way out". That can blow up on you real quick.