Faith
Yes, I am saying that they are not truly Christians
I assumed this to be the case. However, you have not demonstrated how it is you are a christian while others are not.
My definition doesn't have to be authoritative outside my own system for it to be valid, or for it to be valid and not moving the goalposts to state that a practicing gay is not a Christian.
True, it need not be authorative outside your own system, yet this does nothing to support your contention that the christianity you practice is more valid than anothers
as it pertains to the label known as Christian. At best you may call yourself a Christian but not a "true" christian since the establishment of that is a matter of belief and opinion.
If he calls himself a Christian it's for YOU to figure out which definition you want to accept, and since it has implications for your eternal life you might want to consider it carefully, but mine is perfectly consistent and valid.
I disagree. The purpose of language is to communicate. If you fail to specify how you arrive at the position you have that is amenable to being consistent with the exclusion of other positions then at best you have a self referent arguement and hence are not very convincing.
As an atheist I see no evidence nor convincing arguement of an afterlife and, indeed, I sense that such is likely based on an inability to accept the inevitable loss of life and end of existence as a coping mechanism for what is anathema for many people.Thus the implications you warn of are empty of content to such as myself.