The problem is that you want to judge everyone else's Christianity by your own standards, and then call anyone a who does't agree with your standards a "liar".
Too bad for you, because God did not appoint you the definer of Christianity, nor the decider of who is or is not a Christian. And as such, you're just going to have to live without that knowledge or authority.
So you are simply saying, "How dare he ask for people to be honest and not hide their religious affiliations". While I can certainly, by your objections understand why, I am simply saying it should be allowed.