One self-defeating stupidity of claiming Caesar owned all the coins minted in the Roman Empire is that you now have yourself under a burden to account for why Caesar would ever want to resort to minting debased denarii. Why would he want to lower the silver content of what you claim he owned?
Excellent point!
Not only does the act of debasement contradict the idea that Caesar owned the coins, it exposes the fact that the state had to extract value from its citizens in order to function. That alone proves the coins were not just property but tools of exchange whose value was rooted in public trust and use, and that the value they represented was real (that is, not arbitrarily decided for no objective reason at all). Caesar didn’t need to stretch his own silver; he needed to stretch the silver he could get from others. That makes sense only if the coins were already in circulation as instruments of market value, not personal possessions of the emperor.
In actual fact, any government requires a functioning economy to exist because the government is a near perfect consumer, which is to say that it does not produce anything but only converts the production of its citizens into the machinery of state, including a legislature, infrastructure, a military, the court system, and police force. Such governmental services provide real value, but the state does not produce that value itself; it redirects what others have produced by way of spending the taxes it has collected from those who do produce real value. If there is no economic activity to tax, the government has nothing to pay troops, build roads, or enforce laws. So when Caesar debased the currency, he was not manipulating his own money, he was manipulating the value that others depended on, because the state's survival hinges on extracting real value from real production.
Indeed, if Caesar were smart, he would never have debased the nation's currency because it dilutes the ability of the citizens to create wealth, and by extension, his own ability to collect taxes and thus to finance his government and sustain his own power. This almost parasitic relationship that governments have with a nation's economy is, in fact, the reason why governments get into the business of minting money in the first place. A secure money system is the basis for a thriving economy and, by extension a powerful government. Generations later, when the government begins to debase that currency, they fail to realize (or if they do realize it, they do not seem to care) that they are washing the ground out from under their own foundation.