I don’t think their point is to make you feel ashamed for wanting material things. They’re trying to make you understand that instead of buying these material things you don’t need now, you can invest whatever money you have (like they did with the rental properties) and use it to make more money so that eventually you can buy what you want without worrying about the cost.

I find the article was good up until that point, your reasing isn’t wrong, but it isn’t right either so you shouldn’t advise your readers to spend their money however they like without thinking of the future.