Now lets talk about CO2 output of driving around extra dead weight. Makes it worse.
Let's say instead that BMW decided all their car models would be physically 4 seaters, but in order to be allowed to use the back two seats, you had to pay a large monthly "sedan fee". And if they caught you using the back seats without paying, they'd sue you. Would anyone accept this? Likely no. And the reason you shouldn't accept this is the same reason you shouldn't accept the "seat heat" fee.
Either way if I truly think I am right, then BMW, etc should just go ahead with this plan. It should be a money loser for them in the long run. But on second thought why burn all this CO2 just to prove a point. We should probably collectively put a stop to it sooner rather than later.
I wouldn't be so sure, it's all about the price. There's plenty of people that don't have a need for the backseats, and at a certain discount on the purchase price it becomes worth it to have two unusable seats in the back of the car. Think about the extreme case, in which the car is free: there are certainly people that would take that deal.
But you're supposed to get a ticket. Or is it fair game to use public transport for free because you can?
Or to put it in another perspective: carmakers have never optimized for weight at the cost of everything else (as otherwise we'd all be driving around in cars made from titanium or carbon fiber). What's the difference between putting in a heavier seat with a non-functional heater to reduce production costs, and using steel instead of aluminium to reduce production costs?
We're talking about a few grams of extra weight on an ICE vehicle over 1.5 tons, if not even an SUV over two tons. If you put a spare bottle of water in your car you'll most likely have similar dead weight.
Now, I get where you're coming from, but the amount of dead weight this adds is so miniscule compared to the general overhead any modern vehicle carries that making this argument is borderline disingenuous.
But a few grams is definitely not correct. It's probably more on the order of 3-5lbs per seat.
If we don't like the heated seat example, let's use power seats. Those are much heavier than the equivalent seat with manual controls to adjust its position and angle. Granted, I don't know of any car manufacturer gating power seats behind a software lock...
Then we can add in the CO2 emission of manufacturing dead material to place in the car.
To top it all off, no one wants this.