It's bad because making everyone a millionaire by decree, or printing more units of currency is necessarily the same thing as devaluing the currency. Such that the population as a whole has exactly the same amount of buying power, and now each unit of currency is worth much less.
The inflation of the M0 money supply, base money, WILL lead to an increase in consumer prices for everything including essentials like food. The only reason people can try to convince themselves otherwise is because of the time lag between when the money is printed and when it shows up in consumer prices. So when the government quadruples the base money supply and the price of a loaf of bread doesn't quadruple in price, people start to think this inflation is no big deal. Well just wait. That loaf of bread will more than quadruple in price. And it will happen all of a sudden.
The majority of the printed money is going into assets like equities. These have increased massively in value, despite the fact that revenues have not increased that much, or have even decreased. This is a bubble and it will collapse. When that happens, then you will see all those printed dollars. Investors will rapidly divest themselves of their shares and will be putting those dollars into others assets that are seen as much safer investments like commodities including food.
By this point governments have no ability to reverse course, in fact they are committed to exacerbating the situation. Printing money is necessary to plug the deficit of government spending. You could turn off the money supply but it will mean devastating cuts to government spending. So they won't do it. Instead they will start implementing wide-scale, all pervasive capital controls in an effort stop people divesting themselves of the rapidly weakening dollar. This is an economic straight jacket and will shrink the economy further, massively stunting tax revenues, in turn reducing government spending, in turn shrinking the economy further.
Calls to 'tax the wealthy' will be eventually implemented, but there isn't anywhere near enough wealth there to tax to cover the effects of a money supply that has grown exponentially. Regardless new tax bills will be introduced. The very wealthy will have already moved their wealth into non taxable assets, domestic and overseas. (This is already happening). The law makers know this, yet regardless this taxation burden will fall squarely on the rapidly diminishing middle classes and ballooning lower classes. You can read the above again to see exactly how printing money is a highly effective tax in it's own right and it did not require any legislation to write.
At this point the world is caught in an economic death spiral and it won't recover until the currency has completely bottomed out and begins again with a new currency and confidence slowly returns. There is no telling how much long term economic damage will have been done by this point.
There is no magic or mystery here. This is not complicated. It is not new, unknown and to be determined. This will be a carbon copy repeat of exactly the same follies experienced by numerous economies in recent history. The only open question is, much like a coming earthquake, when? The answer unfortunately is very soon.