Commoner, had you, in fact, been trained as counsel you would not lose sleep, any more than you would as a doctor in wartime who saved the life of an enemy soldier who had just been killing innocent civilians, or his comrades. Your training would be that your duty is to whoever is next in line to defend, or next on your operating table. And in practice, that's exactly how you proceed.
It's not for counsel to decide the guilt of the man he defends. That's what the jury is for. And you wouldn't be long in practice before you met clients who you'd be very loathe to meet otherwise. And by ten years you'd have met the vilest of the vile and be defending them. But the vilest of the vile are as entitled to justice as the nicest of the nice.And what's more you'd find that some of the'vilest' had been the victims of mismanagement, to put it politely, by the police, already set upon the idea that they were guilty.
Now, you may say trial by police opinion, or public opinion, is ideal. But the greatest satisfaction as defence counsel, is getting the acquittal, which justice and the client deserve. (When you're prosecuting, you get the same satisfaction in getting a conviction against the odds, too)
And if the man goes down, in spite of your best efforts, you accept equally that justice has been done, for the jury have, properly directed, decided he 's guilty. The worst thing is, whatever the result, to think that you could have done much better. That might give you sleepless nights.