I have to qualify my arguments here. I am neither an expert not comitted to MMT.well it's an explaination how Murphy and others would like it to work. there's a glaring flaw, complete omission of the Treasury in the process of spending, claiming the central bank does this (curiously avoids refering to Bank of England even once), then saying the central bank advances the funds (another name for lending). it pretends the bond markets dont exist, begging the question why was Liz Truss budget such a problem for them? the other major question for MMT proponents is, if tax controls inflation why have we been raising interest rates instead of raising taxes?
which brings us back to reality and our thread question. if MMT were valid, we'd still have to ask the question where should we apply taxes? see MMT doesn't solve anything.
1 The model excludes a number of things, principally the self interest of government. Governments neither wish to be voted out or overthrown. High inflation is generally viewed as undesirable and unpopular. Along with high taxes, so the model says there is no theoretical limit to spending, not that there are no consequences.
2 The bond market crisis could be attributed to the loss of control of inflation. Pension funds in particular were looking for higher risk/higher reward returns to counteract higher inflation. The speed with which the changes were introduced and the lack of consultation exarcebated the problem. It doesn't necessarily negate MMT, although I accept this is a somewhat weak argument.
3 Would the central bank (this is a model hence no Bank of England) have needed to raise interest rates if the government had increased taxes? This was never going to happen I have to admit.
4 The Murphy model ignores international trade, money flows and competitiveness. I guess in simple terms it is all about inflation. I think this is very odd and a major weakness.
If you take a look at US gvernment debt, where is the hard stop on government borrowing? They haven't managed to blow it up yet?
I would also point you back to the Cameron government's austerity programme, which was to save the UK from spending itself into default. Government debt has increased massively since then and yet we still rumble on.