You put "extreme left" in quotes as if there isn't such a thing and its simply a way to malign mainstream liberals. Once again this is the kind of tribalism I'm talking about. All or nothing. Purity tests.
There are leftists in the US to whom equality and dignity are the foundations of their belief system. However, that doesn't represent the whole of leftism in the US and it certainly doesn't represent the foundation of actual leftist extremism in America.
To clarify, I don't think most people that fall on the left half of the political spectrum in the United States are extremists. I think that due to their fanaticism and tendency to be more vocal, the extremists have a voice disproportionate to their actual size.
That doesn't mean they don't matter. It just means they don't represent as many people on the left as one would perceive them to based on social media and mainstream media.
I'm not a leftist extremist. I'm a socially liberal moderate that likes the general idea of free market competition but understands that completely unregulated markets are probably just as toxic and doomed to fail as attempts to form completely planned economies. Prudent regulation can minimize predatory and exploitative behavior.
I think there is a balance to be struck between people having individual freedoms and the ability of the government to take measures to prevent groups of people from making it impossible for marginalized groups of people to live enjoyable lives in the US.
My search for that balance is founded on a desire for equality and dignity. For example, I don't think a city or state full of racists/homophobes should be able to use States' rights protections to establish bubbles where its impossible for certain minorities to comfortably exist.
However, I believe that we are often really quick to take knee jerk reactions and pass legislation that may have unintended consequences when it comes to preserving everyone's freedom, equality, and dignity.
You may choose to ignore them, but there are vocal voices in the progressive movement that are racist and sexist and are more interested in establishing a society that revolves around revenge against white people. Some of them are nobodies, but some of them are influential people in places of power in various industries.
Leftist extremism exists. There are people advocating for violence against white people and men in general on Twitter for a daily basis. Reporting these people usually gets ignored.
I'm opposed to leftist extremism and conservative extremism. People that advocate for violence and who advocate for a new type of inequality are assholes, regardless of how many of their unrelated political opinions I might share with them.
I do, however, believe that the US has more work to do in regards to how it treats many different minority groups. I also believe that white privilege exists. I don't think every white person faces a life-changing situation where they benefit from it, but it happens. In my case I'm not sure how much of an impact it had, but it probably had an impact.