but as it is already, peripheral countries have almost zero ability to set monetary policies. Basically only the US, the EU, Japan and China can do that. The rest of the world is effectively managed by the central banks of the bigs, and even then it is really the US Fed that is in control. He's just ceding what little control the argentine central bank had.
The reason this kind of thinking is popular among the masses is often because the local currency is worthless and subject to hyperinflation. So people see a stable currency in the US dollar, and the central bank of their country constantly failing to curb runaway inflation, and think oh lets just use the USD. Without considering any of the macroeconomic consequences of essentially having no domestic economic policy or economic sovereignty.
In Zimbabwe it's basically all South African Rands and US dollars for instance.