Because it’s an immature understanding of life to vote anything as black and white. Life is full color, and a bazillion shades of gray, besides. Grow up.
No one is "voting" anything as black and white, especially with regard to a question from an objective claim. If the claim is that someone is something simply because they tell you they are and you've disproved the claim with your example then the claim is objectively false.
Maybe you should stop telling people to grow up until you've done so first. In the words of Jesus, take the log out of your eye first.