I think most people understand that old songs have to be taken in the context their place and time of origin. Singing an old song as written is an act of preservation not an endorsement of old values.

On the other hand, a bad line can ruin a song for a modern audience. I do a song recorded in the 1920's called "Tear it Down." As recorded it includes the line "Every time I hit her she hollers 'police'". It's an otherwise upbeat song and rather than put an ugly image in people minds I change it to "Every time I see her she hollers 'police'". Since the joke is meant to be on the singer version 2 works better in the 21st Century. Not PC, just common sense.