Re: Reparations, the principle is that black people in this country have historically been damaged by intentional policies of the US government to prevent them from benefiting from government programs. After the civil war white slaveholders were compensated for the loss of their free labor, the black former slaves were stripped of any land and were then imprisoned for "vagrancy" and forced to work for free in prisons. Blacks were prevented from befefiting from the FHA, GI bill, and many other government programs. Understand: this was done consciously and deliberately by the government.
The Japanese were compensated (although inadequately) for the WWII Internment Camps (for three years), while blacks in this country endured 300 years of slavery (blessed by and enforced by government policy -- see 2nd Amendment). Black Codes, Jim Crow Laws, persecution by the FBI under Hoover, all government actions.
Why are blacks not entitled to compensation by the government that harmed them? And as the the argument that "that was a long time ago", consider the disparity of wealth between whites who have been building wealth for generations while blacks were, in many ways, prevented from doing the same by government initiated (or, at least, government tolerated) discrimination.