The argument I’m going to make here isn’t a new one, but it’s important enough to be restated and recirculated.
I’m not all that old, but I’m still old enough to remember when the acronym was just LGB. From a Christian perspective, the LGB movement was misguided, but at least it was conceptually coherent. Even if you disagreed with LGB advocates, at least you understood what you were disagreeing with. I don’t know when the T became a permanent addition (this Google Ngram suggests the mid-90s), but whenever it was, that was the point the acronym became an unstable compound.
Here’s why. L, G, and B were originally understood in terms of the natural (and normative) sexual categories of male and female. L refers to women who are sexually attracted to women. G refers to men who are sexually attracted to men. B refers to people who are sexually attracted to both men and women. (Remember that ‘bi’ means two; ‘bisexual’ presupposes a binary sexual categorization.) Those definitions are intelligible even to those who hold to traditional sexual norms.
But T subverts all that by demanding that we detach those sexual categories from physical (anatomical) realities. According to transgender ideology, the categories of ‘man’ and ‘woman’ are to be understood in terms of gender identity (which is non-physical) rather than biological sex (which is physical). Yet the moment we do that, the L, G, and B become meaningless.
By way of illustration, consider the widely-discussed Gender Unicorn developed by an organization known as Trans Student Educational Resources. (The following critique can be just as well applied to the Genderbread Person; I leave that as an exercise for the reader.) The Gender Unicorn is a visual aid that is supposed to help us understand and navigate the complex and pitfall-laden terrain of modern sexuality and gender identity. According to the Unicorn, we need to distinguish five dimensions: (1) gender identity, (2) gender expression, (3) sex assigned at birth, (4) physical attraction, and (5) emotional attraction. Now consider the first and fourth of these. One’s gender identity can be ‘man’ or ‘woman’ (alongside other options) but these have nothing to do with one’s anatomy (note how the rainbow icon appears in a thought bubble; it’s a matter of internal self-perception). At the same time, one’s physical attraction, the Unicorn tells us, can be toward ‘men’ or ‘women’ (again, alongside other options). Yet one can only have a physical attraction toward that which is physical. So the meanings of ‘men’ and ‘women’ on the axis of physical attraction must be defined with reference to anatomy.
Hence the incoherence: T (which is concerned with gender identity) requires us to define ‘man’ and ‘woman’ in non-physical terms, but L, G, and B (which are concerned at least partly with physical attraction) require us to define ‘man’ and ‘woman’ in physical terms.