This is simply apologistic but vastly understates the reality. Many of the more "successful" small businesses, ie those earning enough after expenses to split income between spouses are run by professionals, doctors, dentists, veterinarians, who have invested 8-12 years in post secondary education, often 
large amounts of capital to get started in practice, and then lose money for 3-5 years before breaking even. This has to be paid back. Unless you allow them to income average over the many years invested at zero return, then you have to give them away to make up the lost income of those first dozen or so years. Now you are taking it away. So here's the deal. Let professionals income average their post BA lost/low income years over the first 10 years in business or just leave things as they are.