Should We Let Walmart Regulate Itself?

In the last few weeks, we've seen two examples of seeming corporate self-regulation. One is Walmart's decision to end all handgun ammunition sales, and the other is the four largest automakers going around the Trump administration's less stringent fuel emission standards to cut a private deal with California that is closer to Obama era-emission standards. But there's an important overarching question to these two stories. Should companies really be taking it upon themselves to address issues when the government doesn't do a good job policing? Should these businesses be punished or praised?