You don't have to be in law school for very long to come to the conclusion that it's not being a shark that makes a lawyer a slime ball - it's just being bad at their job. As a lawyer you represent the interests of someone who knows, presumably, nothing more about the law than what they've seen on Law and Order. By having an incomplete knowledge of the law, taking hazardous shortcuts, throwing your client's case on the back burner until you "get around to it", not putting in the time with your client or for your client, or a myriad of other bad practices, a lawyer takes advantage of their client. Think of it this way, if a doctor had two possible courses of treatment for a patient, don't you think the doctor has an obligation to explain the treatments, the differences, the costs, the risks, etc.? At least there's webmd for medicine. While the law is accessible to the public, the average person will have no idea where to look to find the information they need, and even if they find all of the relevant law on their own, there's a very good chance they have no idea what it means.
The client doesn't know the deadlines required by the court for filing paperwork or what their options are in regards to a lawsuit or criminal charges. If a lawyer does a bad job representing someone it is highly unlikely that after everything is said and done he'll sit his client down and say, "this wasn't really my best work, but I was busy, you understand, right?" In all likelihood the individual client will assume that their lawyer competently represented them and the lawyer will say nothing to them to indicate otherwise. I'm not talking about the rich and famous, or high powered executives, or corporate powers - I'm talking about the regular Joe who needs some help with an issue.
You may be thinking, "I see how this could be a problem, but it really doesn't apply to me," but it does. Say the tree in your yard falls on your neighbors house - they sue you (but your neighbors are nice and there are no trees in your yard anyway). You lose your job and have to go through bankruptcy proceedings (but I'm self employed and business is great). You want to adopt a child. You have to write a custody agreement. You want a divorce. Your spouse wants a divorce. You want a will that properly divides your assets. You're the victim of fraud or any crime for that matter. You're in the wrong place at the wrong time being accused of something you didn't do. You made a mistake and someone's calling you into court for it. You buy property and want someone to look over the paperwork. Chances are, at some point in your life you will consult a lawyer, and when you consult them you expect that they cover all their legal bases. You probably won't be double checking their work - you hired them because you have no idea what you're looking at in the first place. If they don't offer up the best options to you will you know? What impact might they have on your life without you even understanding the alternatives? You could sue your lawyer for malpractice, but you'd need a lawyer for that too.
A shark of a lawyer may be ruthless, but hire them and they represent your interests. The real sleazeball is the one you trust, who seemed nice when you sat down in their office, but neglected to cross their i's and dot their t's. Despite all the stereotypes and jokes, it doesn't take much law school to figure out that the worst type of lawyer you can be is a bad lawyer.