I’m not a man so I can’t agree or disagree. 

It’s been my experience/understanding that niceness exploded with integration. As soon as it became politically unacceptable for people to outwardly express their disdain niceness became an agenda that was pushed onto school aged children. Female role models and influences began marketing niceness as a way to overcome unjustified discomfort and it evolved into everyone getting a trophy. Before integration, it was a difference of class and those with class who were kind interacted respectfully with those deemed “beneath” them. Nice people acknowledged them
but also ignored the havenots. 

An English teacher once told me that the women’s lib movement was actually the dismantling of masculinity to push niceness onto Americans. He said the goal was to lull the youth to sleep and enrage the men to prison. That’s why “nobody likes the nice guy” I thought he was an asshole but maybe you’re right.