Is a 72-month or 84-month car loan a bad idea?

It isn't automatically bad, but it carries real trade-offs. Longer terms often come with higher rates, you pay interest for more years, and the car depreciates faster than you pay it down, so you can stay upside down for a long time. That makes trading in early or handling a total loss costlier. If a long term is the only way the payment works, consider a less expensive vehicle, a larger down payment or a shorter term with extra payments.