The main problem among left anarchists seems to come when their ideas do not pan out the way they would like because most people do not enjoy being vaguely socially obligated to one another.
For example, a gift economy is just a less precise version of trade & the lack of precision is really only preferred by those who have less to offer & therfore something to gain from keeping things vague.
As an ancap I tend to be wary of anyone from the left because I have seen the mental gymnastics they will engage in to justify stealing (even from friends) when things aren't going their way.