I'm sorry but we already know that cross gender arousal exists and always has existed.
In fact, it existed long before this pseudoscientific term was coined but the simple reason many of us don’t acknowledge the validity of this so called "theory" is because it associates the desire to transition exclusively with sexual arousal and nothing else. In other words, it negates that there is such thing as a transgender identity.
At this point I am going to assume these people think we are stupid.
It cannot be put in simpler terms.