Forbes did the math once and determined that Smaug, a dragon embodied by greed and selfishness, is worth $62 billion. There are 17 people richer than him.
Smaug was shot in the heart and it was a morally good act.
Fyi that math was heavily contested, i agree with the sentiment but a literal mountain full of gold, assuming the market wouldnt crash, would make him the richest person on the planet.
We don't actually know the size of the hoard, though. We know it's big enough for him to sleep in it, and we know the Arkenstone was worth one share of it, but we don't have specific numbers (at least, none I can see). Any valuation has to be an estimation, and any estimation will be contested.
Also, the value of gold today is 75 times that of what it was in the 1930s, which makes it even harder to put a price on Smaug's hoard.
Regardless of the specific number, there is a certain level of wealth and greed that makes it morally good to shoot someone through the heart. Smaug is not the only one to have hit that threshold.