It really doesn't matter whether you provide evidence, have actual experience, know the subject inside out. When you say that something is black they will argue that white is a form of black or whatever. It is utterly pointless.
I totally agree.
They argue that you absolutely can not do something yet all the rules and regulations points clearly to exemptions, exceptions and examples where it is possible.
To the question: could the UK government nationalise or provide state aid to the UK steel industry ?
The answer is possibly, possibly not, we don't know until individual cases are drafted, put before the EU commissioner and tested before the courts.
It does not matter how many examples of where you can't or that have not been allowed, it only needs one example of where it is, or even a hypothetical case where it would be to completely
invalidate the argument that it isn't possible.
Hypothetical: The UK government proposes a state aid package that meets the requirements for exemptions/exceptions and/or is agreeable to the EU Commissioner.
It is definately possible to provide some forms of State Aid under the EU laws, it is merely a situation of whether a specific case falls under the exemptions/exceptions or not.
If you haven't put forwards a specific case proposal, you can not say it is allowed or not.
Stating that you know any and every possible proposal, plan or permutation would not be allowed and arguing that the UK Government could do nothing is a pretty big claim that would essentially require something akin to omniscience.