It's only rational. One of the oldest tricks in the liberal book has been to claim the moral high ground, justifying any and all repression in the name of the greater good. The Terror of the French Revolution was justified more or less exactly in these terms. The abandonment of "compassion" does not actually mean abandoning compassion as a value - it means abandoning compassion for "the enemy" in favour of ruthless and merciless repression, unrestrained by any principle that would be considered normal or primary to a liberal or leftist morality. The abandonment of civility is not a concession of the moral high ground, but the opposite - an usurpation of every right to freedom of thought, belief and action. "We are good and you are evil, therefore hesitation and compassion for you is also evil." This is more or less the idea behind it. There's no "rebellion" there at all, no scorn for the powerful - it is a demand for absolute power.

As to the practical side of it, you can see for yourself what a poor fit for its proponents it really is. Essentially, it boils down to a bunch of spoilt rich kids larping as an exaggerated caricature of what they believe to be "the common people"; as a sort of hoodlums. Everything about these people is fake. I doubt they have a feeling for vulgarity or even much exposure to it, they are just a bunch of overgrown kids that are still trying to rebel against the clean, comfortable and secure environment daddy worked so hard to give them. There's a long tradition of this on the American left, especially since the so-called 60s counterculture. If you read up on the backgrounds, lifestyles and stories of some of these people, it's almost unbelievable.

In regards to how effective this will be, it remains to be seen. I think it's a huge mistake for the left to abandon their "high optics" style. Since its inception, liberalism has been a form of moral tyranny that disallows every alternative because it is "evil". The masses have been internalising this message for a long time. Maybe the social situation in the West has declined so much by now that the left can afford this ridiculous and unprecedented overreach, but I think it's extremely risky for them to be attempting this right now, when it seems like liberalism is in crisis on all fronts - demographic, economic, popular, political, geostrategic and so on. If they can successfully pull this off, they may end up establishing something very similar to a perpetual Maoist cultural revolution, except liberal in character. Personally though, I think the much more likely scenario is that they will instead destroy whatever is left of political normalcy and alongside that the entire Overton window. In the end, it will probably come down to how gullible the last two generations will prove to be and how strong an advantage leftist propaganda will have. If the Left gains a total and absolute monopoly on all information flow and the masses end up defaulting to conformism over realism in every scenario, then a zealous and intolerant left will probably succeed in destroying the last vestiges of democracy in favour of some sort of woke, moralist neoliberalism.