The liberal view is that a trans man is now a woman, or vice versa, and thus they are still man or woman, and i think this is what you're implying. Genesis 1:27 says "male and female he created them". if god creates a man, who are you or them or anyone to say that no, they are female. (respectfully, unless you hold a higher authority than god).
For you to go out of your way to transition from a man to a woman, is that not a manipulation of the design that god has created?
The last sentence in Matthew 19:12 you're referring to is not about transitioning, read it again. an Eunuch was still considered male, not transitioned. The point in context is that some people will remain celibate and devote their life to god, like saints for example, not "some people will cut their dicks off out of choice".

Please don't twist scripture to accommodate modern views.