I think in that instance you can probably balance the disgust at a specific client/case, with the overall benefit of having a (mostly) blind legal system
I guess you must be able to fall back on the fact that everybody has a right to a defence no matter how grave their crime.
Somebody I know had to defend a man who murdered his new born baby by kicking it down the stairs. That trial was in the late 80s and it still affects him a little now.
I was just thinking about this. A barrister doesn't get to choose who he defends. Or prosecutes for that matter.