I am curious why it is considered such a terrible practice? A lot of people don't want to spend time and effort renovating an old property (nor do they have the knowledge or experience to do it well) so there is a market for old but already "fixed up" houses and there are people that make a living doing just that.
The vast majority of house flippers are not doing any kind of real renovation on properties. They are painting, putting on new fixtures, and putting in carpet, and then selling the property for 50% more than their purchase price.