I've already said it 3 times in different ways.
You spend X dollars on a car today in full, versus X dollars spread over X years, you will never spend less overall to buy the car for cash today. If you get any moderate return on your money you are at the very least breaking even while keeping the cash in your control. More likely (based on past trends) you are make some to a significant amount above the cost of the interest in the loan.
It costs more money to pay cash than to get a loan. There may be a change in that sometime in the future, but its not true recently or currently.
The reason for this is because banks have (rightly) realized that, to people with good credit, cars are an insanely low risk to loan on and you can get effectively the lowest secured debt rate available on the market for a car. People will stop paying every bill including their mortgage before they stop making car payments (source unknown but there is a source that backs it up)
Ahhh okay thanks for clarifying. It is clear that you are just being lazy and making a bunch of assumptions. You are sort of taking this "opportunity cost" thing from your wikipedia but twisting it in a number of ways. Sorry but you're not being accurate. If you want to clearly lay out numbers then go ahead. I was clear in the logic.
Here are the errors in your logic. 1) yes, agree re: opportunity cost. That was my point too. As I laid out, the opportunity cost needs to be compared on a like for like basis. You say "if you get any moderate return on your money". No, to be accurate, you need to exceed the cost of the debt, on an after tax basis (the return will be taxed but the cost of the car loan isn't tax deductible for a regular person) for this to make sense. "If you get any moderate return on your money" sure again you are probably thinking "the S&P500 could return more than the cost of the car loan" but that is again lazy because you are trying to compare a risky investment with a risk free one (avoiding paying 6% is the same thing as earning a 6% risk free return).
2) "the reason for this" has nothing to do with banks "rightly realizing that cars are an insanely low risk". YES banks are willing to charge a lower interest rate secured by a car than they are for an unsecured loan aka a credit card interest rate that might be 20% or whatever. That has nothing to do with the price of tea in China or corresponds to how much you are going to earn on your investments. Banks are still making a spread over their cost of funding which is comprised of deposits where they don't pay much interest, to market rates where they can borrow money. They aren't going to loan you money at 3% if their cost of funds is 5%, even if you are an "insanely low risk".
Your whole premise is based on the assumption that one will make more money investing their money in (presumably stocks because otherwise this is a really stupid logic), guaranteed, than they will pay in interest on their car loan. When car loan rates were really low like 0.9% then I could see the temptation to really jump at this. Even though at the time, Maik's money in a money market fund was earning nothing so 0.9% was still paying something more than he would have been earning at the time. When the car loan rate is 6%, it feels even dicier to just assume that your stocks will return more than that over the 5 year period. And again, the fallacy in the logic is not accounting for risk, for the fact that stocks COULD lose 20% over that period too, while you are also paying 6% on your car loan.
And the above is why I asked if you have ANY fixed income investments. Because if your whole premise is apparently based on some nebulous "I will find a way to earn a lot of money on my money" world view then I would guess you are 100% invested in stocks. Or maybe more accurately, you should take your car loan logic to heart and also borrow the full amount you can at your brokerage on a margin loan! Because there, you can borrow a lot more money and "only pay a little bit of interest" while you find a way to get a moderately higher return on your money (by borrowing money against your stock portfolio and investing that borrowed money in more stocks to potentially juice your return through leverage). So you aren't even being true to yourself if you have any of your money sitting in a money market, or a short term bond fund, etc right now.
Don't know how to be any clearer about this but you're making poor assumptions here and thus coming to the wrong conclusion, or at least a misleading and misinformed conclusion