Vampyre I think it's a good thing you started the thread and I think you are right to bring it up. Criminal litigation is a morally complex issue (from every perspective) which very few people outside of the system really understand, so asking questions (and as you've shown, being willing to listen) is a good thing to do.
Criminal defence work is not "easy on the conscience". (Disclosure: I am not a criminal defence lawyer, but close friends and family are and I have studied law and done some non-law work around criminal justice). But the ethical dilemmas it poses are bigger than just "is my client guilty" (as someone explained upthread, if they confess the defence you can run is very minimal and technical).
For example, if my client says that they are not guilty but want to plead guilty just to "get it over with" do they understand what they are doing and the ramnifications of that decision?
What if my client is innocent? Defence lawyers I know says that this costs them more sleep than the other way way around!
It is hard work because it involves dealing with these sorts of issues in very stressful situations and lots of clients are hostile, evasive or obstructive. But it is absolutely crucial work. And for these reasons it is a travesty that funding has been cut to a point where many criminal lawyers cannot afford to live and continue in practice. (There was a thread a few years ago about a woman who was five years qualified and earning 23k a year. That 23k was not just pre tax and pre pension but pre all her expenses to - travel, paying the fees owed to her chambers, etc).