When Cromwell had his portrait painted, he wanted it "warts and all". Posterity does not benefit from bowdlerised versions of history. If a singer (no particular on in mind) was drunk at times, or excessively foul-mouthed, or ignored his audience, then that's part of the performer as well has his generosity, fine voice, and musical skills.

The dead don't need positive or negative criticism: but the living deserve the full story.