The famous French political and economic theorist wrote:

"The law is the organization of the natural right of lawful defense. It is the substitution of a common force for individual forces. And this common force is to do only what the individual forces have a natural and lawful right to do: to protect persons, liberties, and properties; to maintain the right of each, and to cause justice to reign over us all."

Read "The Law" by Frederic Bastiat here; http://www.constitution.org/law/bastiat.html

The simplicity and truth of Bastiat's philosophy of Government is undeniable and his slim book "The Law" should be read by every American. The requires no elaborate construct or lengthy defense. Our government is designed to act in our behalf. To defend for us what we would justly defend ourselves had we the strength. The government was formed to provide us this strength in order to protect our natural rights and to provide for our common defense. If we would always measure the action of our government in this way we would be able to clearly discern when it oversteps it's bounds.

Bastiat measures the lawfulness of government in this way;

"If every person has the right to defend -- even by force -- his person, his liberty, and his property, then it follows that a group of men have the right to organize and support a common force to protect these rights constantly. Thus, since an individual cannot lawfully use force against the person, liberty, or property of another individual, then the common force -- for the same reason -- cannot lawfully be used to destroy the person, liberty, or property of individuals or groups. "

Simply stated; If an act is unlawful (unethical, immoral)for the individual to commit then it is generally unlawful for the government as well. This rule of thumb is directly applicable to law enforcement.