I see a very big similarity between minarchist libertarians and communists (especially anarcho-communists):
a) Minarchists consider the state as a way of preserving “the rules of the game” that should prevail in a free market, i.e. freedom of contract, pacta sun servanda, punishment of fraud, and especially the preservation of private property
and,
b) communists (especially anarcho-communists) consider the state as a way higher classes have of exploiting the poor through the preservation of private property.
I know minarchists consider the preservation of private property as a good thing whereas communists consider it the root of all evil. However, both ideologies share a same underlying assumption: the state is necessary in order to maintain private property. As long as the state and a degree of private property coexist at the same time we must acknowledge that Marxists have a point (or at least we can’t prove them wrong) regarding their consideration of the state.
And this is when anarcho-capitalism comes to play by considering the state not the friend, but the natural enemy of private property. For me, the relevance of anarcho-capitalism is that if a society could exist for a long time without a state and with private property, improving the standards of being of all, including the poor, (as I believe it would) it would tear apart and make senseless those marxist statements. On the other hand, if a minarchist free market society existed for a long time, communists would still have a point (or at least they wouldn’t be proved wrong).
I know some might say that the difference between minarchism and anarcho-capitalism is not so big (all in all, one favours 95% freed markets and the other favours 100% freed markets), and although I somehow agree with that statement, it is also important to note that that small percentage is highly relevant when it comes to disproving Marxist ideologies.