There's no other definition for atheism other than "disbelief in God".
I understand however, and we often come to a clash with what I call "American Atheism", AA's seams to imply some oddities to Atheism, such as same sex marriage, abortion, gay rights and a whole load of dogmatic crap that is alien to Atheism, basically they want to input a sort of leftist view or "caviar-leftism" to Atheism.

Doctrines are bad by definition, because ANY course of action can be either good or bad based upon its context. Doctrine and dogmatic views always follow irrational responses by ignoring this factor.
In other words what's good for me may not be good for you and vice-versa, and what may be good today may be bad tomorrow.

And please! Stop with "falsehoods" and "Messiahs"! That sounds so irrational! Specially taken that you're talking of a religion made by Romans some 100 years after the supposed Jesus existed, if he ever did.