How to spot a disingenuous supporter of a cause.

I find that the fastest way to spot a disingenuous person is to ask him or her directly, "Would you personally support x?"

When that person tries to counter with, "Well, x isn't happening." press them. "That's not what I asked. I asked if you would support it if it were happening."

If you can't get a straight answer out of the person at that point, you can reliably assume that the person is lying to you.