I just gave an opinion to a potential client that effectively said, "I don't think you should go down this path. Here's why. If you do decide to go down this path, then I'm going to have to respectfully decline being involved."
I am generally loathe to do this sort of thing, because jobs ARE hard to come by in the unemployment capitol of America, but I just can't see myself spending two years doing something I know is wrong (misguided is probably a better word), and having to fight the whole way. I had to view the project objectively, and just ask myself, "Is it worth it? Is this going to help me reach my goals? Am I going to learn something that will help me later?"
If the answer is ever a "No" or a "maybe" it's an alarm bell. I'm a firm believer in doing all you can to make money, but if it isn't worth it - it isn't worth it. Fix your eyes on the point you want to be at and work your way backward to where you are now. Don't let anything take you off the path you want.
And when you hear alarm bells - pay attention.