It is not anti capitalist based on any libertarian definition of capitalism I have ever encountered. Konkin's own words:
“Where the State divides and conquers its opposition, Libertarianism unites and liberates. Where the State beclouds, Libertarianism clarifies; where the State conceals, Libertarianism uncovers; where the State pardons, Libertarianism accuses.
Libertarianism elaborates an entire philosophy from one simple premise: initiatory violence or its threat (coercion) is wrong (immoral, evil, bad, supremely impractical, etc) and is forbidden; nothing else is.
Libertarianism, as developed to this point, discovered the problem and defined the solution: the State vs the Market. The Market is the sum of all voluntary human action. If one acts non-coercively, one is part of the Market. Thus did Economics become part of Libertarianism.”
“Libertarianism investigated the nature of man to explain his rights deriving from non-coercion. It immediately followed that man (woman, child, Martian, etc.) had an absolute right to this life and other property – and no other.
All theft is violence initiation, either the use of force to take property away involuntarily or to prevent receipt of goods or return of payment for those goods which were freely transferred by agreement.”
The State has laundered authoritarian & socialist policies under capitalist structures/labels, but that doesn't make capitalism the problem. And calling what is clearly an anti-athoritarian branch of libertarianism, a leftwing movement, really makes no sense given the authoritarian nature of basically all leftwing movements.
Those who claim to oppose heirarchy seem to only be people at the bottom who want to tear down those above them so that they can then violently insert themselves into positions of dominance. Look at the stupid defund the police movement where a bunch of leftists wanted to be given the police budget. They didn't want to end the subjugation of taxation that funds the police, they just want to be the collectors of the spoils. They want to exist in a heirarchy living at the expense of & above everyone else. They want others to be their slaves so they don't have to work.