There's no straw man - my point is that if you don't claim that there is a necessary connection, then your general argument(s) cannot establish that discussion of political topics is wrong speech.
Logically, that doesn't make sense. There are necessities and contingencies. As a Buddhist, I hold that all dharmas are contingencies.
I take it that you do not wish to temper your thesis in that way. In which case, you have to establish that discussion of political topics is necessarily wrong speech.
I already did, not only in the body of the thread multiple times, but in the OP, hence "almost always full of negativity" not "always." I don't know why you make these strange assumptions, you also assumed I was not a Mahayanist -- how much more further should a reader trust your judgement?
But should this be read to cover the very wide terrain of what we now understand 'political' to mean?
I think it's far wider than the term political.
For example, isn't the topic of justice (what is it, how might we achieve this as a polis etc) actually far more important than gossiping about a king or battle? Surely a Platonic treatise on that matter (or something more contemporary) is more exalted than a bunch of people at the bar expressing conceited opinions about Christopher Pyne's evil smile?
It's not gossiping about a king or battle, it's "talking about X" specifically. Gossiping is wrong speech by the nature of the type of speech, not the subject matter. And unless that talk leads to the goal of the path, it's not right speech. Remember right speech is part of the path, we're not talking about a definition of good speech regardless of Buddhism, but as a part of the proper and full practice of Buddhism as expressed by the texts.
And if it is more exalted, than don't we have to make some kind of distinction between what might be lowly and problematic, and what might be important and necessary?
Yes, if it leads to the goal of the path it's right speech. If a certain political speech leads to that, then it's fine. If it's just about services and utilities, you're not on the path.
Also, how are we using the term 'political'? Being derived from ancient Greek, I don't think we can make claims that the Buddha said anything at all about it directly. Might the lack of discursive attention given to important political concepts such as justice, legitimacy, liberty etc tell us something (note, not everything) about why so many Buddhist nation-states have been so utterly unstable?
Well, Buddhism doesn't really lend itself to ideology. Most Buddhist "states" historically modelled on some other system, e.g. Kautilyan, Confucian, Brahminical, etc.
That apathy and not discussing political topics is wrong speech. Since social democracy is arguably the best form of governance so far conceived and only works in conjunction with informed citizens and participatory democracy.