This is an age old question, that can only be answered by turning it on its side.
The only wrong thing stated was: "and somebody who really needs it can't get it because of us". This statement is evil. I will try to explain why after.
Greed is an important driver. Like you said, very little gets done without a motivating force behind it. Growing hunger is probably one of the most destructive drivers. People will eat their seed crop (what is being stored to grow next years crop). Entire eco-systems will be devastated.
Greed is much more benign. There is little that you can do in a fair economy that doesn't benefit lots of people. If you build something that someone else wants because you want money (to get something else) then all the people are better off. Only when you start thinking in terms of limiting other people so that you can have the most, does this break down.
The other part is, stuff. It actually takes part of your life's energy for everything in your life. It all drags you down. Talk to anyone who has lost most everything, and they often say that they felt so free afterwards.
So, a balancing act of what you desire and stuff is essential.
Right now, we could build products that last 100 years. But, if we did, everyone would have everything and most stores would have to shut down.
Someone can't get something because of us. There is enough food, housing and clothing for everyone. It is a fact. However, greedy (people who want to have something at the expense of other people) powerful people have taken steps to keep these things appearing scarce.
After buying a house in a community, they decide to pass a zoning ordnance that states all houses need to be bigger then 2000 sq. ft. (To keep property values high...) but what this is really doing is, those who have gotten a house, are now pulling up the ladders so that the next generation cannot attain what they have.
The idea of guilting people for wanting something is form of evil advertisement. Like, everyone one in America should feel guilty because they have a refrigerator and all the 3rd world nations don't. When, it is more appropriate to say that America got together and built a refrigerator for all of us, and they didn't. We built all the supporting structures, and they didn't.
Now, there was a lot of exploitation going on that kept 3rd world countries 3rd world. But, Detroit had unions and mafia, and that didn't stop them from developing a huge industry.
This sounds very Ayn Randish ;) I agree that nobody should try to guilt you into wanting less. But I would rather discuss the personal perspective, not the forces from others.
I mean, it IS evil. The very statement is soul crushing. The inevitable conclusion from fallowing that train of thought is world destruction.
As in, humans are bad for the environment, conclusion, we should kill all the humans to save the environment. (Ignoring that humans can also be good for the environment)
The only proper way, if there is something that is necessary for life, is to make it as freely available to everyone.
To say that someone shouldn't have something because there are more needy people ... it destroys the efforts of those that would make it, get it made, get its price down...
The statement should be, lets work out how to make more.
not, lets hold ourselves back because someone might need it more.
(then we could get into the conflicts of scarcity vs abundance mindset.)