Cultural normative behaviors and cultural taboos are largely driven by the ancient "fear of outsiders", found in primate bands and tribes, and used to reject any member who deviates sufficiently from normative behaviors.
Our particular culture, the Western heteronormative patriarchy, has established a fairly narrow range of acceptable behaviors, particularly in gender roles and expression, the gender binary. This culture is slightly more tolerant of variations by what are considered weaker or less threatening classes of members, women and children, and less tolerant of variations in the dominant class of members.
The cultural fear is expressed in conditioned responses to unacceptable variations, expressed as outrage or anger. In many persons, an errant positive feedback path exists in the brain, rewarding outrage and "righteous indignation" at unacceptable variations with a flood of chemicals, such that the outraged person is neurochemically rewarded for their righteous indignation.
These persons act as enforcers of the cultural normative and acceptable variations.
Cultural change to bring transgender persons, particularly MtF, within the range of acceptable variations may take many generations, as we wait fro the righteous indignation junkies to eventually lose their addiction or die off.
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