Is it super dumb to finance a vehicle for 72 months?

Indeed.

What kind of rate

Depends on the interest rate. Anything under 2.5% I would finance as long as possible. I make sure I have enough money to pay cash for my car, if the current interest rates are cheap enough I just use that cash to make my payments. I keep a year of cash available and the rest in my taxable account (made over 10% last year).

If you are not financially disciplined enough then no never finance for more than 3-4 years.

I financed my truck for 84 months at 2.75

Let's assume for the sake of argument that we consider financing a vehicle (paying for a depreciating asset with borrowed money, with interest - however nominal) a necessary evil.

The min/maxers will come in here and say, "I can invest the payment and make money on it idiot" blah, blah, blah.

In every...single...case - vehicle financing costs you money in depreciation, period. 72-month is particularly subversive because it allows the folks who right ought to be in a $7500 beater to drive a $50k car because they can "afford" the payments. So, they pay $700 a month for 6 years instead of 1 year.

Pay as much as you can afford down, and finance for as short a period as you can, even if it hurts. Why? Because it's super dumb to do otherwise.

I financed a new Mazda CX-9 for the wife at 2.49 for 75 months last July. I pay way more than the minimum each month and want to get it paid off in 36-48 months. I barely put anything down on it but am already back in the black in value vs. balance.

Helps when my car is a 2004 4Runner that's been paid for for quite some time. I bought that one used and paid it off in 36 months.

In general, it's dumb to finance a vehicle at all, unless you are getting a really low rate.