Before getting all up in other peoples business, would you say the same thing about someone wanting to borrow $20k for a pickup truck? How about a $60k BMW. I sure wouldn't. Right now I'm looking at doing the exact same thing as the OP. I technically could pay for the plane up front, but it would mean spending all of my savings, and having nothing in reserve for those surprises. My truck is paid off, my boat is paid off, my motorcycle is paid off. I have a $150 car payment on my daily driver and the rent on my house. I can easily afford a payment on a plane. Just because it's not a primary mode of transport doesn't make it any different. My primary modes of transport are paid for, why not make payments on a plane instead of a car? It's just money.
When I bought my truck I had to put it under my mothers name because I was young and had no credit. Paid it off and got nothing out of it credit wise. When I bought my motorcycle I had a 783 credit score but no history, so they still required a cosigner. Yep, I financed a "toy", and a pretty expensive one at that. Paid that off in 1/3 of the term and suddenly they were falling all over me to get another loan. I had the cash to buy my car, but I'd rather have that cash in my account for when that awesome deal on a new piece of shop equipment falls in my lap and I need $5k TODAY. Now I have the credit to buy pretty much whatever I want, and I did it by financing a "toy".
Borrowing money you cant afford to pay back is stupid. Borrowing money that's easy to pay back gives you options. It helps your credit, it allows you to keep your own cash reserves, and if you're not paying ridiculous interest rates and you can make the payment every month there's no reason not to. I try to borrow against money I already have. If push came to shove I could pay my car loan off tomorrow, but in the long run I get more out of making double payments every month on a super low interest loan.