I've been reading up on MMT recently, and I haven't seen adherents (e.g. Mosler) claim that inflation is good. They do provide a heterodox account of how government spending leads to inflation, a sectoral one that focuses on demand from the public sector outbidding the private sector in areas were the economy is already at or near productive capacity. And they claim the traditional examples of hyperinflation e.g. Weimar are adequately explained by supply-side constraints. They also explain why austerity has been such an abject failure over the last 13 years in the UK.