Yes, someone will always do it anyway.

You must ask yourself how you will feel about providing professional support to this MLM. Can you imagine looking yourself in the mirror? Can you imagine how you will feel once the job has been completed?

I had a dilemma like this back in 2007. I was an auditor at a CPA firm, and my boss tried to assign me to a new client...a PAC... back when PACs were just starting to register in the general public's awareness. This PAC was in support of a politician that stood for the opposite of nearly every social issue I cared about. I did try to keep an open mind. Auditors are supposed to be unbiased, but usually the worry is don't get too friendly with your clients, not the other way around. But I couldn't do it. I imagined what it would be like to go to this place for 2 weeks to do the fieldwork. And I couldn't do it. Just 2 weeks of my life. Nope. The politician was too polarizing.

I told my boss to assign someone else. He gave me a little flack for it, but overall he was a good boss who appreciated me as a professional. He assigned someone else and that's the last I heard of it... until that PAC was getting targeted by tv talking heads waving our audit report in front of the cameras.

I'm soooo glad I declined that assignment. Not only am I proud of myself for standing up for my issues, not actively undermining them by working for the "other side", but I dodged a bullet by not being associated with them on actual television.