Why are people working for a company allowed to buy Shares?

Recipients must disclose insider buys and sells as a check / balance. Moreover, in many cases, insider trading is illegal and punishable by imprisonment and / or fine.

Productivity and Quality

Most employees do not receive information that can be considered "inside" why should be denied the ability to negotiate in a population from the rest of the public can negotiate (not to mention the fact that the agency theory suggests that allowing employees to buy shares translates into higher productivity and quality, and that employees have a stake in the outcome of the company).