Society is always correct? Um, no. And not just with gender issues. History is filled with examples of societies doing stupid/wrong stuff, even if they "thought" at the time it was "right". Heck, just go back to the slavery period in the USA, and then segregation, 3/5 rule, women not "capable enough" to vote, etc.
As far as the whole gender issue...why is it okay to change other parts of your body (all of you is determined by genetics, etc., hair color, body type, eye color, nose shape), but changing gender or even your physical sex "going too far"? I can change my nose and that's "okay", but if I wanted to adopt a female body (I'm a male), then "OMG NO THAT IS WRONG".
More like society is always subjective and biased. Of course, "society" is just made up of individuals, who are often subjective and biased.
And even if it's a "sin" to change your sex/gender, (most) religions (alive in the USA) also preach that God can forgive sins. So even in THAT light, ostracizing, persecuting, or bullying people that make these choices is not "Godlike". Those same religions preach that God loves all. No where is the caveat "as long as you retain your birth sex and fit the gender role the society you live in says you should fit".
It's one thing to say "I disagree", especially if asked, but it's another to be demeaning and so forth.
It's more like just another variation on "I don't like it, therefore it should not exist" and they wrap it in (a likely misunderstanding of) their religion to justify it.
Nature, credited to God/greater powers in most religions, is a funny thing sometimes. Sometimes our human minds don't grasp it because it doesn't "fit the patterns". That doesn't make nature wrong, it just shows limitations in the mind and our knowledge that need to be overcome.