Dude, it is a single firetruck, not a fleet of firetrucks being driven around to pick up groceries. If he were starting a trend, then yes perhaps this would be a-bad-thing. Instead, it's one guy fulfilling a lifelong dream. The gas mileage is going to be terrible and the emissions bad, but it's one firetruck.
The maxim is simply "if you're really interested in fire trucks, and you can afford one, then you can buy one," and there's no problem with it becoming a "universal law," because very few people will be that interested in fire trucks.
Also, if everyone were to try to buy firetrucks, the price goes up — and makes me wonder how supply and demand fits in with the categorical imperative (if at all).
