Ethics Rules demand that a legal advocate be able to represent any client for any position, no matter his/her/their personal sentiments about the client and/or their position as long as one's personal feelings don't interfere with that representation. Example: If I'm an attorney who is pro-choice and the client is suing to close an abortion clinic, as long as I can put my personal feelings aside and be a fair advocate, there is no reason why I can't represent that client. This is what allowed Clarence Darrow to represent both railroad trusts as well as the proverbial Scum of the Earth.
Now, that being said, looking at the present situation, an attorney at the law firms faces a choice: Quit your firm or represent the client. When a partner assigns a client/case to you, you'd better be able to prove why you can't represent that client -- and most reasons why not fail. (Example: conflict of interest like the client is your brother-in-law or a former client in another matter)
Otherwise, essentially the only thing one can do to protest the law firm taking a case like this is not to engage such law firm for any of your matters in the future. Unless you can lodge an ethics violation, there really isn't much one can do if you're not the client.