I have been asked some version of this question a few times via those who obviously would want to stay anonymous. 

A: First off the good news: 

1. Many bad musical ideas come from the head forcing an unresonant idea on songs. Try to get the artist to express and not force a concept on their music. Most competent musicians understand when ideas don't work and that they can be forcing things. 

2. Many ideas sound terrible when described but feel great when you hear them. I can't tell you how many times as a producer a band has described to me their new direction and I have had to keep a straight face as I hear about how Jethro Tull meets Thursday is going to sound great, only to find out they want to bury a flute part in the mix in a bridge for a few seconds. Many ideas musicians go on about are actually subtleties they are just fixated on. Don't get too scared until you hear a direction in practice. 

3. You can show them music that may have an affect on them, but it can't be with the threat of your lack of support if they don't take it. But being a friend and sending music to those you work with should always be welcome. 

The bad news: If the artist really feels this direction and is making this because its what they feel, that's what they have to do. Sadly this sometimes means the relationship needs to be severed since you are no longer passionate about working with them. This is one of the hardest parts about the suit/artist relationship. It's also why I have feared ever getting any band's music tattooed on me in fear that they could start making white power ska at the drop of an emotional whim.