There are substantive and substantial differences though.
To take your example of NAMBLA: they are advocating for something which a) is viewed as a mental disorder by modern mainstream medicine, and b) is criminalised by all progressive legislatures.
To take the example of transgender people: they are a group whose identity a) is viewed as valid (ie not a mental disorder) by modern mainstream medicine, and b) is protected by law in most progressive legislatures.
Achooalleee... Pedophilia is not, by itself, considered a mental disorder by modern mainstream medicine. Pedophilic Disorder, however, is. There are criteria related to that specific disorder that must be met, and not all people who are attracted to children would meet those criteria. Additionally, pedophilia is only considered a disorder at all in modern times because of the social view toward sex with children. And there are organizations representing "MAPs" that are actively trying to change that social view.
This is a very strong parallel to transgenderism. There IS a mental disorder that is associated with transgenderism - gender dysphoria is still a diagnosis, as is autogynephilia. Both are associated with what people currently consider to be transgenderism. And here's the real kick in the pants - the only reason that transgenderism is under consideration in this discussion at all is because of organizations that actively engaged in trying to change social views of transgenderism.
The only material difference between your "principled" argument in support of transgenderism is the success that those organizations have had. And I'll also note that the success has been gained by intentionally bypassing the public view, latching on to unrelated causes, and by lobbying government agencies while actively excluding the views of females from consideration.
There is no reason at all to believe that the exact same thing could not happen with pedophilia. Your entire argument is based on the imagined authority of the DSM as well as the highly selective actions of a handful of government entities.
If the various MAP organizations are successful in changing the views of governments, and destigmatizing pedophilia... will you alter your position and become a full-fledged supported of MAPs? Will you begin calling those of us who place the wellbeing of children above the sexual desires of (almost exclusively) males "bigots" and "MAPphobes"? Will you come up with a clever acronym with which to insult those who do not immediately accept pedophiles as a "natural variation" o the human condition?
Which is why transgender identity is here to stay (unless/until mainstream medicine changes its view on the matter, which I'd judge as extremely unlikely).
Totally why lobotomies, hysterectomies to control depression, and diagnoses of ritual satanic child abuse are here to stay too. Yep. Makes perfect sense.
Apparently, whatever the psychological community latches on to as it's newest toy is 100% right and cannot be questioned. I mean, who would dare challenge the view of a field with such a stellar history of perfectly appropriate treatments?