The only time you hear this is when MLB does the Jackie Robinson tributes. Some blowhard on Fox will then tie him to the Republican Party and make a big deal about it. Outside of that one time of the year, no one ever mentions it.
I'm not saying nobody does it, but I think it's definitely a small issue. More relevant would be the coopting of Martin Luther King Jr.
Robinson's political leanings became more pronounced after he played. It's a really interesting narrative. If you're curious, I suggest reading Dave Zirin's A People's History of Sports in the United States.
Not me. In school we learned about Jackie Robinson and how he integrated the Major leagues, but the only part emphasized was how he agreed to and didn't fight back. They omitted the part that after his three year agreement of not fighting back ended, he did fight back. They omitted the part about the white press' objection at his change in tactics. They omitted his reaction to the white press and saying that now that he was fighting back, they thought he was an uppity N_______'. That was what was left out in learning about him in school. They painted an incomplete picture that better fit the image they wanted to have of him, and not the complete story. I also heard about his public differences with Malcolm X in Fox news as well as other places. Sure FOX news has done exactly as you said, but it goes beyond just FOX news doing it.
I agree it happens more frequently and pronounced with MLK Jr. But I feel like that's been discussed many times before. Like I said this was something that I wasn't really of until just recently.
This will likely be a wingnut column somewhere by Sunday at the latest: Mandela believed in freedom, therefore, he was a Conservative. Thus, he would be against the Obama administration which is trying to limit freedoms for Americans.