People act in accordance with their notion of identity. There was a study about voting that showed that getting people to identify themselves as a voter resulted in statistically significant increase in them actually voting than asking them if they would vote or having them pledge to vote.

For this reason I take issue with replacing “we don’t talk like that” with “please use kind words”

The former helps form the child’s identity as a person with values, one of which, is not using mean words. The latter is a plea to abide by the parent’s values.

It is not cruel to raise your child to have values and to instill those values. I would argue it is cruel to deprive a child of those core values and replace it with some sort of obedience to authority which is what the updated phrase instills.