His mother had emotional issues and he took some verbal abuse as a child. This led Buffett to go out of his way to be liked by others and avoid confrontation at all costs.
I think he also supported breaking a strike (at the Washington Post). That ain't nice stuff, and I think he vowed never to get into that situation again. But he did get into the first time.
What's not-nice about that? Letting a cartel exploit its customers seems like the moral low ground.