because I don't buy things for their depreciating value
the last new car I bought will be 18 years and a month or two old by the time I get mine, so if I own the Model 3 as long, I'll be getting my money's worth out of it no matter it's resale value.
I'm retired and kids are grown and flown. House is almost paid off. My current car will be 17 years old by the time my Model 3 arrives. My wife didn't bat an eye when I told her last year that I was going to stand in line to reserve it (indeed, she has Tesla-lust almost as much as I do). So, all-in-all, no justification necessary!
My existing cars are a 2000 Insight with a dead hybrid battery pack, roof leaks, failing starter, and nearly 800k kilometers on it. My other car is an even older, even worse shape '93 Ford. I live in a country where EVs have no taxes (gasoline cars are very heavily taxed), gasoline is $7-8 USD/gal, and electricity is cheap and clean (aka, the car basically pays for itself).
1. Needed a second car. Previously we got by as a one-car household, but that's no longer the case.
2. Wanted a Tesla ever since the Model S came out.
3. Wanted a Tesla that could get to LA on one charge (I know, I know, lots of SC's en route, but that was my personal "now it's worth it" benchmark).
4. Preferred a smaller and cheaper car than the Model S/X