The policy that led to a collapse in oil production in a petro state? The policy that led to an economic collapse so severe that 20% of the population has emigrated? That's the policy you call defensible?
The Venezuelan economy was dying before the sanctions.
Burning the economy to hand out free money isn't good for the people.
Maduro and Chavez fixed the exchange rate, imposed price controls, printed money and did a wave of nationalisation (not the oil infrastructure that was in the 70s). USA isn't to blame for Venezuelan dysfunction.
Sanctions go way beyond just direct trade with the US; they attempt to prevent all countries on earth from trading with the sanctioned entity, by force of the USD settling system, or as the past week has shown - the US Navy. So it reduces the number of potential trading partners from hundreds to a handful with (near) reserve currencies, and a navy that's not a pushover.
Also tells you how serious US is with sanctioning russia and its army of oil&gas resellers btw, which is the primary cash flow financing russian war in Ukraine.
Where it failed is that Venezuelans are an utterly corrupt people lacking any sense of nationalism or patriotism.