Both John Lennon and Patti Smith were trying to make a point, no matter how well intentioned, and they both failed. Buffy's analysis covers it off pretty well. Will never listen to either songs again.
Brown Sugar makes no point at all and is deeply offensive. Also will never listen to again. A lot of problematic sexism, too. Under My Thumb and Yesterday's Paper are also now unlistenable, amongst others.
The art vs artist argument is irrelevant to the above because the art fails.
Clapton? Overt racism. Bowie? The infamous wave (Nazi salute) signals a delusional state of mind. Keith "I'm Black" Richards. Being drunk or coked out isn't an excuse. I've spent many years in the arts and many artists are truly awful people, yet they're not alone in this. Sometimes their awfulness tainted their art, sometimes it didn't.
The music industry went out of its way to crush the biracial initiative of rock and roll, enacting a radio apartheid that would last for decades. Not for a second should we let any of them off the hook, but where do we draw a line between art and artist? No Ronettes because Spector was a murderer?
Finally, your thoughts on Bob Dylan's Hurricane, a song ostensibly about racial justice would be welcome.