I assume it's a matter of supply and demand. If clients would demand an honest, law-abiding (specially formulated for you, Ross) lawyer, they would get an honest, law-abiding lawyer. They don't do that, of course. When someone needs a lawyer, he wants the nastiest, filthiest, whore-son he can get. After his trial, he then happily continues complaining about this morally-challenged occupation.
It's not just that. When the U.S. Construction was first founded, they really hoped that 'gentleman farmers' would run the government. However, just as police forces recruit head bangers, and medical schools attract self-important mindsets, politics attracts those hungry for power and the ability to use power in their personal lives. Likewise, the legal profession attracts professional liers.