Why offer it then? Nobody expected that trim.
I'll go back to a statement I made earlier (not sure if it was here or somewhere else), but if a $35K car was promised in 2016, in today's dollars that would be $36,707. Now yes, Elon promised a $35,000 car. I don't remember him making any particular promises about specific trim components (certainly not something like heated seats), but if you expect a $35,000 car in 2019 dollars, because of inflation, you are going to get a little bit less car. Although frankly, heated seats is definitely something I would not expect to show up in a base car. And if it makes you feel better, you are getting a glass roof for that $35,000, and that was almost certainly mentioned as something that would NOT be on the base model (it was advertised as being part of the $5000 PUP package).
Now, the one point worth arguing is whether losing out on $3850 or $5625 of tax credit is a valid argument.
Looking back at expectations in the days leading up to March 31, 2016, and the time shortly after, I'll say this.
Prior to the announcement, the whole reason that I went to the store to wait in line as opposed to just ordering online later that day was because my expectations at the time were that the Model 3 would not enter production until 2018 and not ramp up until 2019 (it was only after seeing the reservations that the schedule was accelerated by a year). In doing my math, I figured that I would have to be near the front of the line to get the full tax credit, given that in that time frame I expected Model S & X alone to trigger the phase out. I fully expected to get the car in either late 2018 or early 2019 (and this is why I had timed a car lease to terminate then). Now while I don't think it was specifically mentioned whether the base model would be offered at the time of release or not prior to the reveal, reasonable expectations would have been that it would not (although I was still holding out hope for a non-PUP release within a few months). So a reasonable expectation for someone placing a deposit pre-reveal was probably around 50/50 (or worse) that the base model would be eligible for the full $7500 tax credit.
Post-reveal the expectations changed. It shifted to Model 3 producting being ramped up in time for a significant number to be eligible for the full credit, although it was also clear by then that the base model would not be the priority. I think a fair assessment of the odds would have been greater than 50/50, but definitely not a sure thing.
So yes, there is some merit to the argument that $35K reservation holders are in effect having to pay more than they expected, but I do think a reasonable expectation was that it would not be eligible. A reasonable expectation would have been that it would have been in time for the $3750 credit, and for a lucky few, this may be the case, but most are going to be in the $1875 time period. Meaning effectively they lose out on $1875. And that gets us back to the inflation argument again...$35,000 + $1875 of lost credit opportunity is $36,875, which in 2016 dollars is $35,160.