In addition to the ethical aspects of the product, I would add, that I always ask myself, "if I was laid off today, can I use my current job to get another job."

I worked at a company where the the work I was assigned was undermining my career to the point that if I didn't do something on the side, I wouldn't be able to pass an interview.

So while the business aspect is important, it is not the only thing that matters; it never is.