Mine is complicated. I agree with Robina except for how we might define the hard left.
I mean, yes, the cancel culture/SJW college/high-school kids are unhinged, I agree. But alt-right is in a league of its own, IMO. Those guys want a Whites-only state. No one on the cultural left goes that crazy, IMO, and I say this as a severe critic of the cultural left, whom I consider often dangerous but not in the sense I consider the Alt-right dangerous. That's why they have things like mass-shootings among adherents. They are only comparable to actual terrorist groups, like Al-shabaab et al, IMO. Not other political fringes, not even the Tea-Party/Far-Right. Even the worst left identitarians on the Democratic side, whom I genuinely loathe and who weaponized woke politics (the weaponizers are typically mainstream too, btw, not 'hard left' at least in the economic sense), cannot be accused of anything on the level of 'White women ain't having babies coz evil Jews,' and 'Blacks/Browns shouldn't exist in this country.' If they are not genuinely insane, these guys are evil. Mungiki level.
I think the problem is many on the Left go so far as to class all Republicans secret alt-righters. But that's a mistake: Just like on the left, there are many different interests on the Right who vote for Trump or the Right in general for distinct reasons, and many who belong to just one or two of these camps. Trump was just wily enough to give each of them something to get them to back him enthusiastically before or after the 2016 general (he has since consolidated some Tea-Party and Corporate Never-Trumpers since 2016, I know this for sure), i.e. He has delivered something for these four interest camps: (1) The Corporatists/Mainstream/Warmongers, (2) Christian Conservatives, (3) Tea-Partiers (the true 'Far-Right' or 'constitutional conservatives' as they call themselves), and (4) Alt-Righters. The wall was for the Alt-Righters, the SCOTUS and Federal judges were for both Christian Pro-lifers and Tea-Partiers, and the war-posturing and tax-cuts have been for the Corporate-backed, warmongering political mainstream.
IMO, there's no Left equivalent for the Alt-Right. The Tea-Party 'enemies' on the left would be the Economic populists. Interestingly, they both oppose both the Dem and Rep corporatist warmongers (who in reality are each others' friendly rivals, not enemies, like they pretend to be to get votes), while the cultural left, you might say, are opposed to/by Christian or just Traditionalist cultural conservatives (I've actually found there are many non-Christian Traditionalists, even from other religions, supporting the Right on the same basis). When you find non-Whites on the Right, they are typically in one or two or all these three camps. Which is why I say the Alt-Right has no left counterpart: their 'enemies' are literally non-White people. It's not just an ideological/policy fight where they take the opposite stances as some left policy, they literally just want the U.S. to be an ethnostate. And like Al-Qaeeda, et al, their ambitions are pretty global: Just anywhere there are white people, these guys want everyone else to vanish. It's no wonder they have so many shooters and lone-terrorists. The best thing is they are fringe even on the right, in the sense that many will not want to publicly get labeled one. The worst thing is they've moved pretty steadily towards the mainstream since 2015, which is super scary.