Not to defend the subsidies, but car making is a capitol-intensive business. Just to produce your first car off the assembly line, it's several hundred million dollars up front. All for a couple of thousand in profit per car (for a luxury car, less for an economy car)...
Tesla got super lucky in acquiring the NUMMI plant. Not only did they get the manufacturing space they needed at a discount price, they got the stamping press and paint shop that Toyota & GM left behind, and that saved them tens of millions.
The other thing to remember about the subsidies (currently $7500 to the buyer) is there's a cap of 200,000 per manufacturer per year. So if the Model 3 is a big seller, some of those Model S and Model X buyers may find they aren't going to get one. Oh, the agony of not getting $7500 back on your $100k purchase!