If I have $0.50 cash and someone reaches into my wallet and takes it, is that any different to if I've got a lottery ticket with an expected value of $0.50, and the draw occurs and its value drops to $0 when it doesn't win?

Some would say that in the first case it's morally wrong to steal my cash, whereas in the latter case I consented to the risk of my ticket losing when I purchased it; and therefore performing a lottery draw is not an immoral act.

Yes, if the Amazon model doesn't work out and you lose value, that's not immoral. It just happened like your lottery. If the value decreases from people stealing from Amazon then it is the same as going in your wallet and taking the cash.

How is this "stealing", if Amazon advertised the price they sold the product at?

Except you did't have $2000 cash because you invested it in Amazon, whose value dropped to $0.

Cash is simply the physical form that the government has deemed legal tender that must be accepted for payment. In the case of countries like 1920s Weimar Republic, that cash can lose value due to hyperinflation in currency trading markets.

/r/iamverysmart

You'd still own the stock even if it was valued at $0. You didn't lose anything.