Speaking as a cop, I say you place the blame where it belongs. My "worst" arrests were a man on his way to his mother's funeral (parole violator) and a woman trafficking drugs to pay for her daughter's wedding. It's not my fault. Sure, there's times you give people breaks, but that's usually for lesser crimes.
Speaking as one who has done a bit of work with attorneys, all I can say is you do your best. It's not possible to do any better than that! Your job is to get the best possible outcome for your client. A lot of times it is the laws, and not the jurors, that are responsible for bad outcomes. If laws need to be changed, and if you feel strongly about it, you can become one of those people who become an "activist," trying to effect change in the system.
And, quite honestly, the world needs more people who are trying to make a difference!
I'm not saying that you go home at the end of the day and forget everything. There are some things that will stay with you. The question is, where do you go from there?
It's not an easy path, but, it is rewarding!