Who decides who is or isn't "following Christ?" Is there a universally accepted criteria for that among the forty-two thousand sects of Christianity? If you claim the WBC members aren't real Christians based on your subjective interpretation of Christianity, can't they say the same about you?

There's no similar subjective interpretation of atheism. Belief is a binary state: you either believe or you don't. The only nuance to it is why you don't believe.

Obviously there isn't a universally accepted criteria for atheism either, because there are people who believe in God who claim to be atheists. Why is a universally accepted criteria necessary?

You're absolutely determined to redefine atheists as people who can also believe in gods. Why is that?

I'm not, I'd say that definition is silly. I think we should be able to say people aren't in a particular group even if they say they are.

There are over forty thousand different sects of Christianity based on something like seven major doctrinal disagreements. They all give different weight to different doctrines and scriptural interpretations. They all claim to be Christian and none have yet successfully demonstrated that they have the proof that they are true Christians or that others are false.

On the other hand, atheism is just one thing: a rejection of claims regarding the existence of gods.

Do you see the difference?

Atheism is defined by us as the position that God does not exist. But some people who claim to be atheists and also believe in gods presumably define it differently. Are we justified in saying that they are incorrect, and not atheists?

If so, we are also justified in saying that people who claim to follow Jesus but do not are not Christians, regardless of what they think.