Yes, I agree that we should recognize the history of people being dicks. However, all that some groups want to remember today is white people being dicks, and black people solely being the victims.
the quickest way i can explain what you're missing is in a comic: http://i.imgur.com/1S139Cq.jpg
the longer explanation? the U.S. owes a lot of its current position as the leading economy on the backs of black slaves. yes, there were white indentured servants, too. the vast majority of enslaved people were black folks. and we're talking about generations of black people made to work under a white majority.
explain to me what happens when you continually subjugate one people over centuries and many generations? to the point where that people have lost almost all of their economic, social, and political power? just "freeing" that people does not even begin to repair the damage. just saying "hey, you're free and equal now!" doesn't magically wave away centuries of destruction.
and in fact we know that the whole equality bit has not even come true. from Jim Crow to the striking down of significant bits of the Voting Rights Act, to the almost daily extrajudicial police executions of unarmed people of color, racism hasn't actually gone away. and white persons still benefit from it
here's the part where you protest that "hey but I'M not racist!" on a conscious level, sure. great. but you still benefit from that racism. i'm making the assumption that you're white simply because if you were black, you would know. your perception would be different. you would not be inherently afraid of police. you would not mistrust schools or "traditional" forms of career advancement. you would not have to exclude certain neighborhoods when considering a home for fear of being unwelcome. there's an entire world of which you're unaware.
so instead of complaining that you're not part of the problem, listen instead and come to realize it's not about you. it's about a society that has an addiction of breeding success by treading on an underclass.