In our world of constant scientific breakthroughs in the analysis of DNA, etc. frequently we read of cases being overturned based on NEW evidence that results in determining the innocence of people incarcerated for years or, worse, put to death. The "Central Park 5" is a perfect example of this. What nightmares haunt their original defense attorneys now knowing their clients were innocent?
Personally, I would rather see guilty persons occasionally escape punishment than one person who is innocent incarcerated or worse.
It is not the job of a criminal defense attorney to determine the guilt or innocense of the client. In fact, most attorneys will not, purposely, ever ask their clients if they are guilty. Their job is to provide a defense for the accused who is innocent until proven guilty. I believe that good defense attorneys have to resolve these issues in their own minds early on in their careers. Those that are unable to come to grips with it can easily continue to practice in other areas of law.