Your statement "not so long ago, African-Americans were treated unfairly" can't sensibly be interpreted multiple ways. What you meant to say might have multiple interpretations, but what you actually said can only be interpreted one way, unless one is to distort the words past all reason.

"more specifically, it used to be commonly accepted that black people weren't as intelligent as white people." I'm unfortunately unable to find any surveys which show to what extent this is still believed by people today, but my impression is that this is still a far more commonly-held belief than you think.

"And if you downvote my comment, please explain why." Well, in this case, I'm downvoting because you're whining, because you made an assumption about who downvoted you based on little evidence, and because you've written a post that doesn't say what you now claim you intended it to say and are now blaming the readers for your own mistake.