Me buying food from restaurant would make the owner richer, but would also employ more people at the restaurant.

The scarcity issue is valid when the resource is limited. In case of US, I was not aware of food scarcity. Even housing is more due to policies than actual land scarcity.

Economic activity does have positive feeback. Yes, some people get unfairly rich - but the solution is not to stop the activity, instead try to get the rich pay their fair share of contribution to the country.