There is a big difference in dressing up as a rabbit or friendly obese white man on the one side and dressing up as a black man using stereotypes that originated from an era where segregation was normal.
The whiteman stereo type is not a negative one, the blackface stereo type does have a negative origin. White men have never been oppressed, been looked down upon as inferior or been exhibited in a zoo(not so long ago: http://www.doorbraak.eu/gebladerte/11507f99.htm in dutch)

The discussion explodes every time because of the underlying problem of the racism that still lives strong. Dutch people are more racist than they are willing to admit. They still feel superior. it is not just 1%. 1% does not get mr Wilders and his Princenvlag friends enough votes to sit on the pluche.

Children do not care, that is what the experiment someone else talked about illustrates very nicely, they just want a fairytale to believe in and they will believe whatever you tell them and show them, if you dress up as someone else, they believe with their shortsighted minds that there is someone else and the other person is gone. They will fill the gap with their vast imagination. If Zwarte piet changes their minds will accept with no hessitation. It is the racist parents and adults with their fixed unimaginative brains that do not want to see that change is not a problem.