"Going bad" wouldn't mean singing other types of song for people who aren't into folk music.

It'd mean sticking with folk music and cheapening it down by playing it without respect for the songs and the people.

Singers who broaden out into other types of music, either because that's where their tastes take them, or even just ("just") to make a living, can still retain their folk roots - and they can be a route by which people who think they don't like folk music can find their way into it, and discover they do.