I think a good role model is someone who knows what they want from life and makes choices that support their vision for who they are. A parent like this sets an example for their kids that says, "be the best YOU that you can, whatever that may be". So if someone's calling is to stay at home with their kids and they are brave enough to do this in the face of the judgment of others, I say good on them. They are setting an example of strength and being true to who they are.
Similarly, someone who goes to work instead of staying home with their kids will be setting a great example if they approach their work feeling inspired and do the best job they can every day.
It's when someone loses themself and their dreams that they cease to be a good role model. That can happen to bored SAHM's and disengaged employees equally.