I'm guessing that the lawyer gave him advice on how to proceed, and may well have advised against it. But if Evans is aware of what he is doing and insists on proceeding, the lawyer can take the case if he doesn't feel that it's unethical to do so (ie, he has explained everything and the client wants to take action anyway). If the worst that is likely to happen is that he'll lose the case and have spent some money on lawyers for no gain, that probably happens all the time and wouldn't be a big deal.
As for the potential fallout from such an action, that seems as if it would be Evans's fault, not the lawyer's. His insistence on making everything public, combined with his inability to control himself, is creating a mess that is entirely of his own making.