It has nothing to do with free enterprise or competing with business, when you seek out your ex employees customers, you are not competing, you are simply stealing, and in many cases customers do sign a non compete employee clause, when they sign many of the service invoices and contracts, in most cases a non compete contract, will have well defined conditions, the purpose of the contract is not to prevent an ex employee from seeking other work, or even operating his own business, it's main purpose is to have some protection, if he walks away with the company customer base, which is private property, he will have to open his business the old fashion way, work for his own customers, not steal them from, a previous employer.