Should cops be able to turn on their sirens just to avoid red lights, and then turn the sirens back off?

Police are given different level of responses to different type of call....typically referred to as Code 1, Code 2, Code 3....depending on the emergency or issue they are responding. Depending on the department, they are normally given some latitude to intermix different aspects of the code to get where they need to get. Anytime a Police car is going to violate/ exceed what a normal citizen could do in a car, normally state law requires the Officer at a minimum to activate the emergency lights and sometimes the siren. Ultimately, the officer is always civilly and criminally liable for their actions while driving...e.g. they do something the violates the typical driving laws. A typical call that officer might have been en-route to would be like a verbal domestic or argument. Since no knowledge of active violence going on, they would not be authorized for lights and sirens...but since the likelihood of violence could occur, their department may allow them to put the lights on to clear an intersection when safe to do so, to get to the call in the most expedient manner possible.

Do as they say, not as they do

Being on a department now, I can say that it completely depends on the call. Some types of calls we feel do not warrant running code for the whole trip. But, there are certain times when we cannot guarantee people's safety while we wait at a red light.