Isn't the whole concept supposed to be the size and volume beget efficiencies and therefore getting bigger should make you more profitable? Amazon revenues have what, tripled over the past 5 years, but as you rightly point out, their operating margins have declined substantially. That flies in the face of logic and the drive for growth.
The company has been in business for 20 years now and hasn't really generated any profit. If they are now investing for the next 10-20 years, at what point does "long term" actually happen. At some point you have to show the ability to be profitable.
Curious - if you are basing you investment thesis on the idea that they can turn profitable when they stop all the growth spending, when do you see that happening? The company acknowledges that the cost basis and capex will continue into the future. At some point the time it takes to get there more than offsets any level of profitability that they could even theoretically achieve.