I think the salient point is that there are extremists on both sides but the article only concerns itself with right-wing extremists. In effect, this isn't a campaign against "extremism", it's a campaign to combat right-wing extremism while left-wing extremism continues to proliferate unfettered.

The OP characterizes this as a cultural revolution, but I don't think he made a particularly good case for it. Notably, I think "passively tolerating left-wing extremism while cracking down on right-wing extremism" is pretty weak evidence for CR. Rather, I would argue that CR begins when left authoritarianism begins--when the mainstream, majority viewpoint (the Overton Window) takes a back-seat to the left-wing extremist viewpoint due to intimidation.

If I were to argue that we're on the brink of a CR, I would sooner invoke cancel culture: threatening to get someone fired for espousing mainstream viewpoints (e.g., advocating for nonviolent protest or Tweeting an interview with a black man concerned about black-on-black crime). I would invoke BLM riots (no, I'm not talking about peaceful protests) and a media that refused to challenge the predominant narrative with obvious questions (e.g., "How are we collectively so sure that the cause of the shooting disparity is 'racist police' and not some other factor, to the extent that we are ready to burn neighborhoods to the ground rather than entertain dialogue?") and instead spent months rationalizing the violence. I would also note how remarkable it was that nearly every business in the hardest-hit areas were quick to hang "This business supports BLM" or "PoC owned business" signs, while their suburban and rural locations felt no such compulsion. I would invoke surveys showing chilled speech in newsrooms and the academy or an explicit willingness, pride even, from the same institutions to discriminate solely on the basis of politics.

Ultimately though, while left-wing extremism is concerning, I'm less interested in arguing over the threshold at which it becomes "Cultural Revolution". I think we should content ourselves to note that it is fundamentally illiberal and anti-human and continue advancing the causes of peace, justice, equality, and prosperity.