I understand that this is an atheist site and most who post here are atheist but I also don't believe that it is being religious that creates bigotry.
It's just easy and cheap to blame someone's religious affiliation or lack thereof on any opinion they hold that you disagree with.
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Except phand's prediction is objectively accurate, and that is because it was based upon the highly evidence based premise that Abrahamic religion is the world's #1 causal promoter of hateful bigotry toward the LGBT community.
Notice the hateful FB post by these parents that got the most "likes" explicitly references the Bible and throws some Bible based hate for gays in there as an added bonus.
And they are not "abusing" or "misusing" their religion but using it as designed and intended. They are objectively correct that the Bible commands them to be intolerant toward homosexuals and implies that God made only man and woman and would not have made "mistakes" that humans needed to correct with surgery, which thus makes transgenders an insult to God. The Bible and Koran were written mostly to spread bigotry, intolerance, and justification for violence against those deemed outside a set of narrow and arbitrary authoritarian rules. Plus, the very concept of a monotheistic God who sets all the rules is the epitome of authoritarianism which inherently promotes intolerance. These parents are the Christian honestly using their religion as designed and intended by the intolerant bigots who created the religions.
It is not some magical coincidence that strength of religiosity and these forms of intolerance have strong correlations at every level of analysis from between individuals within a society, to within a society across different time points, or between different societies. Yes, there are some tolerant people who self-label as "Christian" or "Muslim" but dishonestly cherry pick from their religious texts and disbelieve much of it while actually getting their morals from secular culture. But that does not change the fact that Abrahamic monotheism is in fact THE #1 source of hateful intolerance toward those in the LGBT community and the greatest cultural enabler and promoter of racism and misogyny. What it means is that self-labeling as a "Christian" has little meaning because it often is just a superficial label that doesn't reflect whether the person actually believes the core ideas of that religion or derives their ethics from those ideas and founding documents. To point to tolerant "Christians" as evidence that religion is a not a cause of bigotry is like concluding that smoking is not a cause of lung cancer by pointing to a friend who smoked a pack per month for a year and hasn't gotten cancer yet.
And in anticipation of a likely "no true Scotsman fallacy" type of response, reference to that "fallacy" is itself the far more common fallacy. A Scotsman is defined by simply being a man from Scotland. You either are one or not. Thus, pointing to a belief or behavior that doesn't fit an expectation as evidence they are not actually a Scotsman is a fallacy. In stark contrast, being a Christian or Muslim in any psychologically meaningful sense is defined by one's beliefs and actions. Thus, it is completely valid and in fact logically neccessary to use one's beliefs and actions as the evidence of whether one actually is a Christian or Muslim, and to recognize that people vary greatly in strength and sincerity of those beliefs and thus in the degree to which the category applies.
After all, we have a number of people I consider to be bigots who are also atheists on this site. And I've been assured by some of these wonderful people that I am the bigot and racist.
Questioning whether a trans-person with a penis should be able to use a public shower designated for "females" is not an expression of hatred toward trans people. You cannot point to a single atheist on this site who has ever come close to implying that a transgender person (let alone a child) should be violently mutilated simply for being trans. That is because the level of violent bigotry without reference to any actual harmful actions by targeted person is rare outside of the context where the bigot can rationalize violence to enforce arbitrary rules by deferring to the mandate of some unquestionable authority who's whims decide the rules (e.g., monotheism and other fascist dictatorships).
Also, LGBT bigotry is a special subclass of bigotry with almost no other motive outside of religion and enforcing of arbitrary authoritarian rules. Such bigots have very little to lose or fear by treating LGBTs with equality and respect, outside of the fact that it threatens ideas at the heart of Abrahamic monotheism.
Thus, such bigotry is tied to religion even moreso than racism or misogyny, which each do have other selfish secular motives where the bigot personally benefits by treating women or various racial groups as inferior and less worthy of resources like jobs, education, political power, etc.. The fact that the Bible and Koran were written to promote such misogyny and tribalistic bigotries does make these religions major causal promoters of them, but the relationship is not as strong as between monotheism and LGBT bigotry.