This is kind of the tl;dr 30-second elevator version of it.
Hegel's Dialectic is at its simplest the belief in a positive idea (the thesis), a competing negative or contradictory idea (the antithesis), and the end result, a new concept that nullifies and replaces both the thesis and antithesis, the synthesis.
Social Marxists, cultural anthropologists, and other leftist thinkers have loved to rely on the Hegelian dialectic to attack Western thought for many years. Edward Said (a literature professor) wrote the famous book "Orientalism" that basically says everything that Westerners believe about the Middle East is pure fantasy, wish fulfillment, the Other; that which the West is not. The West is civilized, therefore the East is savage. Western women are chaste and virtuous, therefore Eastern women are sultry whores (harem fantasy). Western men are honorable, Eastern men are untrustworthy, etc. Said, incidentally, just built his book on the prior work of everyone's famous pedophile, Foucault.
Ok, getting to the point.
Today, why do leftists of all stripes love drag queen toddler time? Why do they love kids burlesque shows? To reference a post from today, why do leftists NPCs love cities and hate suburbs.
Thesis. Antithesis.
The left today is defined entirely by what the right is NOT. To be more accurate, the left today defines itself in opposition to their perverse imaginary view of what the right is.
The left believes the right is Christian, therefore the left exults in atheism, satanism, Islam, etc--anything that is NOT Christian.
The left believes the right is ignorant rural and suburban dwellers, therefore the left is modern and urban--anything that is NOT rural.
The left believes that the right requires strict gender roles and rules, therefore the left wants to tear down the very concept of gender.
The left believes that the right wants to kill all gay people, therefore the left wants to groom more children to be gay.
Edit to add: The left believes the right is irredeemably racist and white, therefore the left exults and honors anyone non-white over anyone white.
Edit to add: The left believes the right is male-dominated and patriarchal, therefore the left attacks anything masculine and praises the feminine.
Some of these points are a bit (but only a bit) exaggerated, but the point is that the modern left is an entirely intellectually bankrupt movement. It is a negative. It can only define itself as the opposite of the right.
Also not really their strategy. Leftism is just deconstruction and postmodernism. That’s really it. And that functions by taking existing value hierarchies and militantly inverting them. That’s why it’s easy to predict what they’ll do, and why they’re basically evil in one way or another. If you view all value hierarchies as things to flip, you’re basically on the side of evil in somewhat of a literal sense.
Wanting gay people to get gay married or not is one thing. Leftism is wanting them to get married BECAUSE the traditional value hierarchy would say they shouldn’t be. That gay marriage is preferable to traditional marriage BECAUSE it goes against traditional marriage, not because there’s merit to it or not. Or with the body acceptance for women thing. Plenty of the girls held up in that are actually hot, but that’s not why they like them. They just want to put someone up as hot BECAUSE traditionally that same girl wouldn’t be idolized for beauty.
It’s all that on repeat. There’s no dialectic going on. Just postmodern deconstruction. They’re not trying to synthesis new ideas from a productive critical exchange, just flip whatever traditionally worked.