One of the reasons there is a need for lawyers is that laws are often vague, despite attempts to not do otherwise. Take the 8th Amendment - it puts a ban on cruel and unusual punishments. But, there is nothing that explains what Cruel and Unusual means. Hence the need to parse it out.
Some people will argue that we should retain the standards that were in place in 1791 (strict constructionists). The theory is that if the American People want something to change, then they will band together and petition the Government to make such a change. Of course, with Bureaucracy, this is fallacy, but many people believe that until we tell the officials to change the rules, then we should keep things the same. One very real problem with strict constructionists is that they are only strict constructionists with regard to the laws and rules they think should remain the same (Note the Activist decision on minimum pricing a few months ago).
There are people who argue the "living constitution," that the Constitution should be interpreted to meet the mores of America today. These people note the inefficiency of Government, and how times change much more quickly than laws. They think that one of the roles of The Court is to act as a gap filler, and that decisions that reflect today's world are the best solution. The problem here is that a living Constitution can ultimately be little different than rule by public opinion, which is difficult to follow for any sense in the world.
There are other approaches, but I'll leave it at these two for now.
The Supreme Court recently granted cert on a case in Kentucky challenging Lethal Injection, claiming that the chemical cocktail used causes undue pain in the person being killed. This has had the result of Texas planning to stay executions here until such time as the Court renders its opinion (because Texas uses the same cocktail).
There are a couple arguments at stake here, but all of them revolve around the concept of "what is cruel and unusual?" First, there's the concept of the chemical cocktail. Is it cruel and unusual to cause undue pain to a person who we are killing? People have spent centuries trying to come up with a humane way of killing people (Guillotine), despite the obvious oxymoronic nature of said attempts. This is up to 8th amendment debate because lethal injection was not a method of capital punishment at the time the Bill of Rights was created. Second, and probably not the question that will be answered, but undoubtedly at the crux of the issue, is whether or not Capital Punishment qualifies as cruel and unusual. Here's where the debate between Originalism/Strict Constructionism and other theories comes in. According to one strict constructionist argument, since we had capital punishment at the time of the 8th amendment, then it cannot be considered cruel and unusual, until Congress passes a law or amendment defining capital punishment as cruel and unusual. And those who embrace a living Constitution and oppose capital punishment would argue something similar to the concept that in America today, it is unnecessarily cruel to put someone to death, or that capital punishment is only a deterrent to the person being killed, and we can keep that person from killing again by putting him in prison for life, making capital punishment unnecessary altogether.
While we wait for the Court to reach its decision, let's see what you think...