Just Governments and Bare Plural

Solution 1:

I think it's a matter of opinion or preference.

I would interpret it as singular. In this case specifically, I can't think of any government that would consider itself unjust. But if all governments consider themselves just, and different governments operate differently, then not all governments can be just... So the question uses the plural to refer to all governments who think they are just, saying to each individual government, "Hey you. You are(n't) really just because just governments ought(n't) require employers to provide a living wage."

In essence, the debater is tasked with creating a utopian "just" government, and, within that government, determining whether it should require a minimum wage.

Edit: That said, you could cite multiple real-life governments that support your claim.

Solution 2:

They amount to the same thing.

We could express it in the singular, the plural (as you have it) or with the uncountable government as in "the practice of governing":

A just government ought to require employers to provide a living wage.

Just governments ought to require employers to provide a living wage.

Just government ought to require employers to provide a living wage.

In either case though the ought suggests a requirement. If it is an absolute requirement that a just government require a living wage from employers, then that applies to all just governments.

Conversely, if there is a government that could be considered just but which does not require this of employers, then it is not a requirement of any just government; though this would not rule out the case that a government could do so and also be just.

The plural, the singular and the uncountable therefore each express an argument that applies to all just governments. All forms therefore require the speakers to address not just multiple governments, but all of them (or at least, all that are just). That said, the actual arguments made need not have multiple examples; an argument for the motion could refer to a single abstract concept of government while an argument against could both do that and also pick a single real example that it claimed was just despite having no such requirement; the single counter-example suffices to dismiss the general rule.