This is actually a very complex issue. I haven't read Sanders' stance verbatim but from other things he's said, I'd not be surprised if I might agree with him. I'd have to see it first, of course. But I do know that I disagree with the notion that anyone not into individual reparations is thereby racist. I think that's nothing but stirring shit.
Maybe at times shit needs stirring to keep the conversation going but you don't do that at the expense of your ally.
Liberals have very much been in the fight for reparation-like policy. Why do I so phrase? By numbers alone; rather not alone, but on both sides of the equation.
Besides that you've got numerous generations going back to slavery that reparations when divvied up might amount to a snow cone per person. Regardless, you've also got that situation in this land of immigrants. That all makes it a little tough to pay out individually. It makes more sense to correct where possible inequities at the institutional level, be that access to education, jobs problems, housing help, etc.
How can you make pay everyone who has come to this country, since, say civil rights of 64. So round off since 1965 there's been 36.5 million new immigrants making home here and since the 13th Amendment was ratified 100 years earlier, there's been 73.8 million new immigrants and now add their descendants, so you've got a huge portion of America--there's only 318 million now, so probably the great majority--who never directly benefited from blacks oppressed and certainly did not institute it nor purposely partake.
Sure you can argue benefits at the societal level but how do you, say, tax an individual to pay for reparations when neither he nor his family lived here during the offense?
So there's good argument to "repay" institutionally, to have society work towards fair opportunity. And liberals have worked towards that. I've no doubt that Bernie will continue that good fight. If he's no intention to hand out individual checks, if that is the argument against him, to pay out reparations at any level less than institutionally, and then to call that racist, I think is not only a mistake but also it is reprehensible and it is self-defeating.