Sure, pedantically I used the word "margin" wrong. The fundamental argument is still sound though: Tesla's profit per Model 3 is ~$8k (~20% of ~$40k), while their profit per Model S/X is ~$25k (~25% of ~$100k). So Tesla is currently diverting ~8% of their Model S/X profits toward the SC network, but they would have to divert a whopping 25% of their Model 3 profits towards the same. The former may be sustainable, while the latter is almost certainly not. So either they will have to make SC access a $2k a la carte option (which may drive a significant number of would-be buyers to ICE's, or at the very least cost them sales of other profit-heavy options), or else they will have to change their unlimited-access model. I know that if I were a price-conscious Model 3 buyer, I'd vastly prefer $0.25/minute supercharging over a $2k upfront fee.
I simply don't understand where the $2,000 figure is coming from. Right now Tesla sets aside $500 per car. If anyone has evidence they are off by a factor of four, they should be screaming to the SEC.
For the sake of argument though let's say it will double over the next few years to $1,000 per car. Right now, GM is spending about $1,000 per car on ads with an average selling price below $40K. That doesn't include whatever their independent dealers are spending on ads that also comes out of the selling price.
Tesla spends $0 per car, and is estimating an average price of $42K per Model 3. I may be off base, but I don't see Tesla having to spend any money on ads before 2019 or later to drive demand.
If GM (and Ford and FCA for that matter) can spend $1,000 per on ads, why can't Tesla spend $1,000 per car on Supercharging. Supercharging not only makes their cars much more useful, it generates tons of publicity. Heck I wouldn't be surprised to see nice big signs visible from the roadway that said "If you had a Tesla you could get free electricity for your next road trip here" pop up. Well maybe not quite that tacky, but you get the point.
Look none of us, has access to Tesla's books, but there is simply no evidence that Tesla can't afford to continue the current Supercharging program.
If it turns out I am wrong and Tesla can't afford it, then they would have to go to an upfront fee. Collecting $0.25 a minute for the 2 hours a year you will be Supercharging won't generate the upfront capital needed to expand the system. Either Tesla pays the upfront costs out of the sales price, or buyers pay it upfront when they buy the car.
If you are concerned with people who live near a Supercharger using it for daily charging, there have to better ways than setting a fee per charge system.
For example, we could continue to let Tesla deal with it; or, Tesla could insert software that would turn your car horn into a speaker that would broadcast "I am a moocher who uses a Supercharger for my daily driving" whenever someone Supercharges locally. Or insert your own non-sarcastic idea here that doesn't involve a fee per charge.
End of Rant.