Calling a transgender person "a transgender" and a group of transgender people "transgenders" is similar to calling an Indian person "an Indian" and a group of Indian people "Indians".

I've yet to see any rule on such language apply across all LBGTQ populations without issue. Don't speak with such authority on issues which has no authority.

There are differences in usage. For example, it is not correct usage to call someone “a French”. The adjective “transgender” seems to work similarly.

> For example, it is not correct usage to call someone “a French”.

Only because the established term was "a Frenchman". There is no such established term for the group under discussion.

What's wrong with that? I'm a Spanish man and I wouldn't be offended at all if I were in a group was referred to as "Spaniards" or "men".

I was arguing that both are equally correct.