Trying to decide...MSW or PhD?

What are some pros and cons? I know that the interview panel is going to ask me why I want a PhD as opposed to the MSW. I don't see myself being a university professor down the line. However, I do want to make a difference by being a policy analyst or program planner -- especially in relation to child welfare and foster parent recruitment and retention. What is the benefit of having a PhD in being a policy analyst/program planner as opposed to having an MSW?