For me it depends on where I'm performing, how I personally feel about a song, and whether I consider it a good song to start with. It's a funny thing but some people are very quick to take offense at the most innocent of songs. Moral outrage is a popular indulgence. I've very rarely had anyone tell me I upset them with a song I've sung. I always give a short introduction before all my songs and it includes noting, if that's appropriate, that the song comes from a time when attitudes were different. It's probably a bit more tricky if you are male and wish to sing a song that supports wife beating. I don't think I'd be brave enough. I sing songs about drunken Victorian fathers but the sympathy is with the victims not the father and that's different. It all depends on your audience and the way you put your songs across.