In response to #8, attorneys represent guilty clients all the time. Attorneys who do not want to do this do not practice criminal law. Everyone, innocent or guilty, is entitled to a zealous defence, and most of the criminal attorneys I know have no ethical dilemmas or difficulties whatsoever.
I think it depends on whether we are talking about business or personal ethics. The idea that a law firm makes money for its services while presumably looking out for the best interest of their client doesn't really present an ethical dilemma. In most cases, providing the best services possible is the way to earn money. Basic business models tell us that in a competitive market, you have to provide the best services to remain competitive and continue to gain clients and make money. Depending on the case and situation, it is not always as simple as that, but I don't think there is a huge ethical dilemma. The one exception might be death penalty cases. The cost of dealth penalty legal representation is astronomical and not likely to provide a profit to the lawyer.
As far as personal ethics: I think lawyers face this dilemma everyday. Do you take money to strenuously represent a client who may be guilty? Once you become their lawyer it is your job to represent them as best you can. It is what you are being paid for and it is the law. If you as a lawyer have moral or ethical issues with your clients behavior, it can be a difficult road to travel.
Law firms and lawyers provide a service to their clients. Yes, they have to do this while keeping the client's best interest in mind but this must be done within the constraints of the law. A defense lawyer has an ethical duty to represent the client with vigor, anything less is unethical.
All licensed attorneys must abide by a code of ethics. The fact that they earn money by providing their clients legal services does not in any way conflict with that code of ethics. As a practical matter, how would an attorney be able to eat or keep a roof over his or her head without charging for those services? Is there any conflict in a doctor providing medical services because he or she charges for those services? Should not attorneys, like anyone else, be entitled to compensation for their work?
It is an attorney's job to provide legal protection for their clients. This may require thinking long and hard about personal ethics, but it does not really involve business ethics. They are in business to provide a protection that is actually stipulated by the Constitution, whether or not their clients are the sort of people they'd want to model their lives after.
Business ethics and personal ethics are two different things. Businesses are in business to make money. They need to look out for their shareholders as well as their clients. As lawyers, a firm does need to look out for the best interest of its clients.
Usually the ethics delimma revolves around lawyers and firms turning a blind eye to illegal activities of their clients because they want to keep their business. Some say that it doesn't matter if a lawyer knows their client is guilty, because the system dictates that all parties should have access to legal representation. I tend to agree with them in principle.
I can't really say that I have. However, I do not really see a huge problem. The sorts of clients that big law firms serve are smart enough to know if the law firm is padding bills with unnecessary services. If law firms do this too much, they'll lose business. So I don't think it's that much of a problem.