I don't know what public defenders make in Iowa, but I know a 5 year one in Colorado makes in the 60-70k range and will often have a case load above 70 without getting paid overtime. And a lot do it because it's consistent with their ideals.
An in-law of mine is a public defender in Minnesota who only works on cases appealed to the Minnesota State Supreme Court for instances of gross miscarriage of justice.
Said relative could be pulling down $150,000+ easily in private practice.
...but instead, as one of the top public defenders in the state, makes like $72,000. The lifestyle and feeling that you are doing some good for the world is worth the difference.
Some of that involves defending homicidal manics, but the veracity of their guilt is rarely in question with these cases. It is more about seeing the law properly applied and procedures properly followed, which we should all favor even for the most heinous of criminals. Jeffrey Dahmer and Ted Bundy deserved what they were legally owed, too.