Just how much of a role "anti-colonialism" played in the lives of father and son is a matter of interpretation, but calling an attack piece "fact checking" implies that the "fact checkers" are doing something more than pitting their opinions and interpretations against other opinions and interpretations.
"Fact checking" allows propagandists to get on their high horse and turn differences of opinion into ethical violations.
That said, I think D'Souza is on the wrong track, and if he really claims without evidence that Obama was preoccupied with the problems of native Hawaiians in his younger days or "coached" in "oppression studies" at Punahou, it does work against his thesis.
There are a lot of "of course" assumptions that people don't question. It's not hard for a reporter to nail these things down if he does his homework, not doing so cuts into a writer's credibility.
Did any liberals care about fact checking Farenheit 911??