From my point of view, Marglin is very close to presenting a post-modernist view of critiques of the mainstream, that is, several alternatives to the mainstream are acceptable, as the much as the mainstream is. This is Deidre McCloskey's view that economics is about the rules of conversation, rhetoric. I'm more of a realist, I think there is an external reality independent of my views about it, and that there are, besides logical aspects, facts that allow us to discern between theories that are not correct (the mainstream) and theories that have not been proved wrong (classical-Keynesian). For my view on heterodoxy read this.
PS: Marglin's syllabus here. Thanks to Pedro Américo for the tip.