Over at the Adam Smith Institute, Tim Worstall attempts to answer the question "what are public sector unions for?" Unfortunately, coming from Worstall's ideological position, and building your argument upon strawmen and (deliberate?) misconceptions, the wrong answer is almost inevitable.
He starts off on fairly firm footing. He gets "what unions in general are for." It's a fairly objective description, too: "they are the banding together of the workers to make sure that the employers do not oppress them." Further, he acknowledges that "such freedom of association is just as important in a free society as freedom of speech." Fair enough. I can't quibble with him on that point because I'd make the same argument.
Where things get ropey is here:
But government is the wise and benevolent looking out for all of us isn't it? At least, among those who purport to support public sector unions it does seem to be. That's why they tell us that ever more of our lives must be determined by government. Yet more regulation , nudging, prodding, of us to do the right thing. As determined by the politicians, those wise, benevolent and disinterested beings who determine what the regulation, nudging and prodding will be.
This assumes that supporting the right of workers employed by the state to combine equates to supporting the expansion of the state and its encroachment upon vital freedoms. But such an assumption is a non-sequitur.
More accurate would be the argument that public sector unions and their supporters support the preservation of public services and welfare which benefits the public, whilst not necessarily defending the functions of state beyond this. This would be, for example, why it is possible to support an institution such as the NHS whilst opposing (say) the war in Afghanistan and the Trident nuclear missile programme. Not a difficult concept, you might think, but its one that seems to continually evade the entire right-wing.
This same blinkered view is behind the common rightist refrain of "shouldn't anarchists support the cuts?" But this is much like asking if we should support constant reductions in take-home pay on the grounds that we oppose the wage system. It's a nonsense, cooked up by people who only see abuses when they are perpetrated by the state.
So, no. Supporting unions in the public sector isn't synonymous with supporting the state in all its endeavours. Hence the redundancy when Worstall asks "if government, politicians, are indeed those wise and benevolent beings, then why should those who are employed by them need protecting from them?" Public sector unions have no such illusions in politicians. Thus, "mak[ing] sure that the employers do not oppress them" remains the goal. Which should really go without saying if you're not trying to demolish the arguments of an opponent you've constructed yourself for rhetorical purposes.
Proof that this line of reasoning is driven entirely by liberal ideology comes from what follows next. Worstall argues that "those of us subject to government" should be able "to refuse to perform under the contract we've signed." Which presumes that society and the relationship between state and citizenry is built upon "social contract."
This is complete nonsense. State power is predicated upon a monopoly of violence, and if "those of us subject to government" want protection, we need to organise - exactly as workers do against an employer. This is the basis of political organisations, community campaign groups, or the kind of revolutionary unions advocated by anarcho-syndicalists. The "tax strike" advocated by Worstall is the rebellion of the more privileged - the middle classes and petty bourgeois - an inherently individual action which most people don't have the resources to undertake (and, in most cases, simply can't do because of Pay As You Earn).
The resistance of working class people is collective. Direct action, not simply to withdraw from a contract that doesn't exist, but to force the state to concede to our power. It was on this basis that the welfare state came into being, and it is on this basis that every victory we have ever won came about.
For Worstall, if "government are people we need protection from [and] thus public sector unions are necessary," then "government is dangerous, we all need protection, and we certainly shouldn't be campaigning for it to have ever more power over our lives." This is something I can agree with, with the caveat as explained above that we aren't actually campaigning for any such thing.
However, by the same exact logic, if we need to compine "to make sure that the employers do not oppress" us, then employers are dangerous. We all need protection from them, and we certainly shouldn't be campaigning for them to have ever more power over our lives. Freedom is a universal concept, and so what applies to the state applies equally to any other body built upon a top-down structure and claiming a monopoly of force over a given area. The argument against the state is also the argument against capital.
Moreover, whilst public sector unions are campaigning to defend not the state but confessions won from it, Worstall and his co-thinkers are campaigning in defence of capital and it having ever more power over our lives. Not only that, but by opposing the concessions we've won and advocating a return to its traditional role, they are campaigning for a strong state whose force stands behind that private power.
Liberalism is the defeault ideology of capitalism. When Tim Worstall, the Adam Smith Institute et al speak of freedom they are making philosophical excuses for the social order that dominates all our lives. That truth, like Worstall's strawman version of the purpose for public sector unions, is "not an argument that I'd want to have to try and defend in public."