But by doing so they are "aiding and abetting" a racist society by enabling racists to listen to music they desire, from people they desire. If they choose not to it makes it harder for racists to be racist.
It's very hard (indeed, practically impossible) to say that X culture existed because of Y culture - in reality they were all tangled up in each other and likely self-reinforcing. In reality X causes Y causes X causes Y causes Z causes Y causes X.
Which IMO is the case if we're talking about the 50s cover phenomenon - the covers arose out of pre-existing racist culture, but said racism was allowed to more easily persist itself via the covers, which allowed radio stations an avenue to provide black R&B (that the audience clearly wanted) without forcing people to confront the fact that it's black R&B by relabeling it and dropping an all-white cover band on it.
The success of said white cover bands (who were able to get much more airtime than their black counterparts, because duh reasons) was also used to reinforce the superiority of the white covers over the originals.
Sadly, a lot of things have feedback loops built into them, it makes untangling cause and effect pretty hard.
Not sure how familiar you are with the phenomenon - it's all rather fascinating, if not a bit depressing to study. It wasn't so much that black bands weren't being listened to - they were, some managed to chart, and they were at the very forefront of a generation's changing preferences. The (to some people, alarming) popularity of these bands is what prompted the covers in the first place, in large part driven by concerned parents who feared their children listening to black musicians, but were under the gun to provide an alternative outlet for a new generation whose tastes were markedly different than their parents'.
I think there's a pretty strong case that the cover band phenomenon made it easier for existing racism to persist - though of course that's not particularly quantifiable - in any case I think it's not particularly farfetched to say that the whole phenomenon was harmful.
If you're interested in listening to some concrete examples (all of these are on Spotify), the aesthetics here are fascinating:
Sh-Boom by The Chords, covered by The Crew-Cuts (whose band name clearly wins the award for "least subtle reflection of society's fears in the 50s")
Tutti Frutti by Little Richard, covered by Pat Boone (who was a central figure in the cover phenomenon, and largely built his career on covering and out-charting a vast number of black musicians)
and because we just celebrated Back to the Future Day - Earth Angel by The Penguins, covered the Crew-Cuts (again with them!)
Its not simply white people performing black music, that is wrong, but rather that the white people filled a demand for black music that could have been supplied by the original culture were the market not racist. Its like, no direct racism, but making racism easier? If those white people had said "No I will not play this music", then the market would either have had to listen to black muscians or not get the music at all.