Two things...
Moderates are kind of wedged in there between conservatism and liberalism. And tangently, there are also libertarians which fall either between moderates and conservatives, or tangently are considered moderates within their own right. However, moderates are typically a label reserved for people who are conservative about somethings and liberal about others. Or perhaps even libertarian about some things as well.
Leftism is pretty much a broad term for anything politically left of the mainstream. You might argue everything mainstream is left, but this is not true. If it were, we would not be allowed to talk to one another.
In America, Leftism is often defined as a liberal extremist. Someone willing to sacrifice their own privileges' to enact the changes they claim to desire. It is fair to think that that is exactly what is happening in regards to covid with vaccines and masks; however, this isn't true if the scientific evidence continues to support their reasons. This doesn't mean you should pursue any scientist who makes a counter-claim as speaking truth or having alternative facts. Not every study or expert has the same credibility as any other. The consensus of data will always be the more truthful than the outliers. And while outliers can become the consensus, until that happens, we have to rely on the best data we actually have.
Second, the phrase "left of communism, socialism, and fascism," means they're actually beyond those those things, or worse than. It would be more accurate, at least grammatically, for you to claim that leftists ARE for communism, socialism, and fascism. Unless you really are saying leftists are worse than these things. Not sure how that can be true.
And perhaps there are leftists (or political extremists) that want these things but a majority of Democrats are against communism and fascism. I can't say how many are against socialism, but they've repeatedly outvoted (and outnumbered) Democratic socialists.