Actually, not so much.
There's not only debt, there's who debt is held by. Japan's national debt is very heavily owned by the Japanese. If I remember rightly, it's something to do with the way the Japanese people have invested in past decades, much of which is heavily in their own government's bonds. If they want to come and collect, they crash their own country: they're not likely to do that for obvious reasons. Most countries could not have so much debt: Japan can, because of who its creditors are.
The USA has very low external debt, because it's such a big and relatively insular economy it largely lends and borrows internally. Smaller countries tend to be much more internationalised and hold much larger external debts (although are likewise often major international creditors, too). Here again, even major multinational finance corporations are likely to blink before they crash economies they are highly invested in, dependent on, and especially the one they are primarily based in themselves.
I don't forget the demographic trends. My argument is that the existing neoliberal model is not going to survive the coming decades because it will cease to serve our societies effectively. The capitalist class and the capital markets are going to have to find another way, or have another way forced on them. They'll resent and oppose it because they've been left to roam free, get intoxicated on Ayn Rand fantasies and think of themselves as Masters Of The Universe for decades. But if, when, our societies come for them, they're going to find out they're nothing like as powerful as they thought.
We can pay for healthcare, UBI, all that stuff whilst we get over the demographic hump: just not if we leave arsehole billionaires free to strip our economies of absurd sums of money that they keep all to themselves. Trump, Brexit, Pegida etc. are in large part forewarnings that it's no longer just the left looking to take them down a peg.
