By definition scarce means limited, and there is a limited amount of food, therefore food is scarce. The fact we throw some of it away is irrelevant - food that is thrown away is not food that most people want to consume, and so for our purposes isn't food at all. If food weren't scarce, we wouldn't have to pay money for it. Air would be an example of a good that's not scarce (unless you're, say, underwater). Certain "Free" newspapers may or may not be scarce, depending on who you are.
A "need" is typically an informal term meaning the highest-ranked want at any given time. I eventually will "need" food, though right now I do not need food, since I just ate.
Even in the layman's terms, "need" is generally conditional. "IF I am going to get this job, I need to do an interview" or "IF I am going to live for another year, I need to eat/get an operation/etc". So we still need to think in terms of cost/benefit, even if that benefit is extending one's life by some period of time.
If housing prices were significantly lower, there would be a shortage - more people trying to buy than willing to sell. Observe: rent-controlled apartments. And if houses were free, most certainly I would get one... but who's taking on the cost of building it? In reality, there could not possibly be such a thing as a free house ("free" in econ terms), even low-cost or low-income housing would require paperwork, a lottery, or other non-monetary costs on my part. But they are still costs for the sake of our supply and demand curve.
What do you mean by greed? Taking other people's things by force is never appropriate, but that is not greed, that's theft. Getting an idea for something, and taking time to acquire it, build it, or trade for it, is very much good. My "greed" for more free time combined leads me to hiring a landscaper. And so on.