Guy was good at what he did. He represented the scum of the earth, but even they deserve advocates. We live in a society, as George Costanza would say.
Shargel's career is an example of how money buys "justice" in America. If you're like 95% of defendants charged with murder or manslaughter, you're probably too poor to afford any lawyer. You'll be assigned a public defender, who'll immediately advise you to accept a plea bargain to a slightly lower charge. But if you have money--a lot of money--you can get a high-powered criminal lawyer like Shargel, or Bruce Cutler, or Barry Slotnick, or Johnnie Cochrane, or Oscar Goodman. Your chances of being acquitted, or of having the charges dropped, improve dramatically. That's because trial law has nothing to do with innocent or guilty, or right or wrong--it's about who wins and who loses. Not for nothing are opposing lawyers officially called "adversaries." Lawyers hate to lose--especially prosecutors, who usually have ambitions to go on to higher-powered law careers or judgeships. If you have Shargel or one of the other criminal law superstars, prosecutors most likely will try to avoid going to trial, probably by offering you a sweetheart plea bargain.
Judges are part of that, too. They hate to have convictions in trials where they presided reversed on appeal--it makes them look bad, and can squash their chances to get appointed to a higher court. If you have enough money to hire a Shargel, they know you also have enough money to hire legal scholars to go over every page of the trial transcript, looking for "judicial errors" that could hurt their careers. They'll bend over backwards to approve objections or motions made by your lawyer, or to find reasons to dismiss your charge on technicalities.
Moral of story: it's good to be rich.