Of course there is nothing wrong at all with disagreeing- or even saying 'yes, I think you are AIBU- hopefully with a reason why.
As several have said, there are ways and ways of doing so. One way is a reasoned disucssion, the other is just plain and simple, unpleasant 'attacks' - as said, by the usual culprits.
It's sad and unpleasant. So be it.
The OP btw is not a problem at all for us personally as grandparents- but was a general statement of concern about the over commercialisation of Christmas, the influence of advertising onn kids- but mainly the pressure put upon parents who have very little, to compete to avoid 'mocking/bullying' for their children- and the debt some families get into which puts massive pressure on them for the rest of the year.
You can't see it, disagree, that is fine. Again, there are ways and ways- as well you know.