Sure, but the point is that your green had better outweigh your red overall or else you have a problem. No one is arguing that there should only be green block

Sure, but the point is that your green had better outweigh your red overall or else you have a problem. No one is arguing that there should only be green blocks - clearly some of the profits that make those blocks profitable come from the spending of people who live in areas that are red. So long as the net outcome is green then everything works out. When you build endless sprawling suburbs that cost more to maintain than the tax base can raise from the businesses that serve them then you have a recipe for long term decline.