I like the way Jefferson Fisher explains it, he’s a trial lawyer, one of the good ones. He says:
“Stop being nice at the expense of being real. Nice protects the image. Kind protects the relationship. Kind tells the truth, even when it’s uncomfortable. Nice won’t.”
The problem is a lot of people don’t want to hear the truth. The original thought is that perhaps it’s more kind to ignore them than to be fake. Not that a nice smile to a stranger or Good Samaritan act should be dismissed. People still deserve to be valued, of course.