Red has represented many people who were wrongly accused, and has derived much satisfaction in saving their futures from being destroyed. Police and prosecutors have a lot of power, and can charge and convict just about anyone. Individuals are helpless against it, and only a seasoned lawyer like Red has the ability to rightfully fight to protect his client.
Being a criminal lawyer requires a substantial set of skills beyond being a good trial lawyer; criminal lawyers must be good negotiators, investigators, counselors, and much more. Red knows his job entails dealing with all of the stressful aspects in his client's life at that moment, not just the accused crime.
One thing is for sure, being a criminal lawyer is a very important job.