Just like it doesn’t work to try an ecosystem based on one species, a society has to blend government and private spending. They work on different incentives and timeframes, and both have pitfalls that the other might handle better.
But what governments often can do, is break local optimums clustering around the quarter economy and take moonshot chances and find paths otherwise never taken. Hopefully one of these paths are great.
The difficult thing becomes deciding when to pull the plug. Is ITER a good thing or not? (Results wise, it is, but for the money? Who can tell really.)
Well, at least VCs don't burn through my tax money, whilst they are failing at picking winners.
See how IBM was on the path to inventing electronic computers for business and accounting, but got pre-empted by the militaries' needs and procurement.
In the counterfactual if there hadn't been a war going on, presumably businesses would have had even more needs for international business machines.
Military/government procurement provided the demand for which private entities could provide, money and other resources at level that private market never managed.
Without large injection of money supply there's not much extra dollar to chase and safe investments sound like better bets.
This provided demand for products and services that simply was not there in private form, allowing way riskier investments - all the way to 1980s Silicon Valley was mostly riding downstream of military procurement (Can't source the quote right now, but Sun microsystems be-or-not-be was landing a contract for NSA for Unix workstations - because NSA could frontload an order for few hundred if not thousands workstations)