Fred Rogers was a Presbyterian minister. In the 1970s, that fact was a source of embarrassment to some of my fellow students at a Presbyterian seminary.
They tended to be students committed to social justice. Some of them came from active participation in the anti-war and civil rights movements of the 1960s. At least one fellow student's name was on Richard Nixon's "enemies list," because of his anti-war activities.
For some of them, Fred Rogers' great sin was that he was just too nice. Christians, they felt, were called to aggressively confront evil, to challenge the powers-that-be.
Put in the terms of classic Reformed theology (although I don't remember any of them putting it this way), Mister Rogers seemed to deny the doctrine of human depravity, to ignore the need for human repentance, as he told each child that he liked them, "just the way you are."
But Fred Rogers knew something of human depravity, as it is experienced by many children. A chubby pre-teen, Rogers was teased about his weight. As someone in the movie explained, "Without 'Fat Freddy,' there never would have been 'Mister Rogers.'" (How much did the name-calling hurt? Throughout his adult life, Rogers weighed himself daily, thrilled to announce that he kept his weight at exactly 143 pounds.)
"Mister Rogers' Neighborhood" made its own stands for social justice, in its typical quiet way.
One scene, from the 1960s, shows Rogers sitting with his bare feet in a child's inflatable wading pool, spraying his feet with a water hose, talking about how good it feels on a hot day. The neighborhood policeman comes by and Mister Rogers invites him to take off his shoes and socks and join him with his feet in the pool. The neighborhood policeman was African-American, and at a time when many American swimming pools (not just in the South) were restricted to whites only, Fred Rogers made his own stand for social justice known.
When all is said and done, Mister Rogers was not simply about being "nice." Fred Rogers, the Presbyterian minister, was advocate of mercy, grace, and love.