No, it's not.
> What proves MMT is in any way ‘factual’.
Factual is class of statements, opposed to normative statements.
> MMT is an old lie
It can't be that old, since it only describes the constraints on sovereign finance of entities functioning in their own pure-fiat currencies, which isn't a subject that has been of interest for very long.
The old lie is that sovereign entities (note the deep and old roots of that term in feudal societies) can debase their currencies with zero consequences.
Usually this works well for a long time, until all of a sudden it doesn't.
They're asking for supporting evidence for MMT.
dragonwriter seems to have meant "factual" in the sense of "concerned with questions of fact", "is" rather than "ought", and was not intending to claim (at least in that statement) that the answers MMT provides are correct.
gray-area seems to have interpreted "factual" as "accurate" or "truthful", and was objecting that defining a theory as "concerned with things which are actually fr-reals true" is cheating.
To be fair to gray-area, "true" is probably much more common a use of "factual". On the other hand, the broader context was that dragonwriter raised the point in objecting to argument about what MMT purportedly says we "should" do.
Factual is entirely off base as a descriptor and has been picked here in an attempt to make it seem grounded in reality and without challenge.
My point here is not to defend MMT but the quality of the conversation.
If someone comes along and says Modern Moo-netary Theory says we should to build too many catapults, and another someone points out that the theory doesn't address questions of "should", pointing out that the theory talks about spherical cows in space doesn't rescue the original objection.
That a theory makes unrealistic assumptions is absolutely an appropriate objection to raise, but it belongs upthread. Otherwise it won't be seen by people who've already decided what they think of the narrower topic of this subthread, and we'll get more repetition of worse arguments.
My objection is to people talking past each other rather than engaging (whether intentionally or unintentionally) and remains as relevant as ever.
MMT is an old lie, oft repeated, and only discovered as a lie after it is far too late.