If the political system only allows the governing coalition a realistic chance to gather the (political, financial, social) resources necessary to mount a viable campaign capable of capturing a majority in the legislature, then it's not a fair political system even if the actual process of the election is "free". Voter suppression, rigged constituencies and seat distribution systems, financing laws, qualification thresholds, ballot access rules, disenfranchisement, etc. And even if the initial elections are free, if the dominancee of one party becomes so entrenched that voters are increasingly apathetic (i.e. schooled into learned helplessness), then clearly something has happened to make popular participation seem unattainable.
I rarely intervene to state this case, but this is the second instance of it here, and as I agree with the non-historical point and its the second instance I've spotted, it is kinder to make it here with someone I agree with outside of historiography:
Political science is not historiography. What is desirable is not historiography. Political science or speculation of what is desirable is not a bad thing, but it is not a historical thing. We do not speculate on the desirable, or what abstract qualities like "freedom" are. We merely note them as theoretical constructs when using them theoretically in historiography (and cite why they're relevant theory); or, we conduct the history of the theoretical constructs themselves. The better way to have put this would have been to cite the theoretical tradition that places popular participation and the realistic chance as the grounds of claiming something to be free, noted the agreement, and then observed if the case was met or not. And then allo-historically have used that to generate speculation.
Some PSI and PCI members on the ground did not consider the Italian state to be a terrain of struggle (using Gramsci, someone known to them culturally), as evidenced by their toleration of an illegal periphery whether Anarchists, Operaismo, Maoists, or Guns Locked Under (or without) Party Key. This seems to indicate that the debate arising within Italy was not over whether Italy was a legitimate state or not, but rather than control over the state (or its abolition) was a more central argument than what the composition of the next cabinet would be from a body of parties considered by a significant membership of the voting public to be ununelectable was.
Now sadly in terms of the original question, the opposition of a large body of the population of a state to that state isn't necessarily an indication of the "authoritarian" category, one which I think I've previously raised the historiography of arising from American institutions funded directly by government: to say it is a political category of theory.
In comparison I couldn't argue that Monty Python funding radical queer liberation groups is evidence that the vast majority of labour voters considered Parliament illegitimate, even if as traditionally in the c20 irrelevant.
While the DC had american political support and the financial backing of a lot of interest and the support of the church at the same time the PCI had the support of the URSS (they have took money till the collapse of the URSS) and the financial backing of the various cooperative (that in the italian context are basically medium to big industry and communist or socialist like the actual Chinese communist party) and the support of the various union so they were hardly at an uneven level.
I think it is arguable whether the evenness or unevenness of funding is relevant to the system being "locked" depends in part on whether the PCI used its even position to attempt to take (in coalition) the System as it was, or sought a system as they would have. Even with a PCI interior minister, the PSI cabinet would not necessarily be pursuing the broad aims of the PCI—such would be a matter for the PCI's own internal politics, one that I'd strongly suggest was divided on the matter 45-89. The presence of a legalist tendency in the PCI adds incredibly to the argument that the Italian political system represented the interests of the brokers of power by their active participation. Kind of like being a Tory under ununelectable Whig governments. You may never achieve a government position, but Lordship is ensured, right after the next Fiat plant is established to placate your constituents. (And if not obvious, I'm arguing here for a power-dynamics analysis of history that incorporates self-interest at different organisational scales, with a concept of "buy-off" brokerage politics, and the idea that participants own theory needs to be read in the light of their actions, or their theory read rather through their actions.)
yours,
Sam R.