Re. Bowie, no all is not forgiven.
Bowie said something stupid in support of fascism. Very stupid. But it didn't provoke the kind of visceral, nauseous urge to vom the way these comments did:

""I come on very strong... That's why black people love me"

"My dick is sort of like a white supremacist. I've got a Benetton heart and a fucking David Duke cock"

For what it's worth, I enjoy reading the novels of Wyndham Lewis and the poetry of Ezra Pound, both of whom espoused fascism at one point. I think Bowie's albums "Low" and "Heroes" are fantastic.

From what I've read about the private lives of the Beatles, Miles Davis, the Stones and Led Zeppelin, none of them were very pleasant people; hasn't stopped me loving their music.

Frankly, if John Mayer made really amazing music, rather than big-chart-rawk muzak, I'd probably end up putting it on and guiltily enjoying it, despite thinking he was a total asshole. Fortunately I'll never fact that quandary in the case of Mr Mayer.