Interesting mix of comments here. Generally, I don't care what the job or who the customer is, and have done all flavors of campaign signs, rallies, churches, even naked chicks (but not porn), etc. I'm in business to make signs for anyone who comes through my door and have yet to decline anything due to a personal objection, until yesterday.
In this case, I'm not sure if you'd call it a moral objection because it's not a controversial issue like abortion, just something that having my hands in would make me personally feel dirty. I'm not trying to be a crusader for a cause or make a statement, and it'll be a silent rejection if I decide to pass because another shop will gladly take the job. Makes me feel like I'd be making a sign for my own proverbial noose, just for a bit of money. Good for the business, but for the squirrel behind the curtain, not so much. Hence the dilemma.
Since someone brought up the Holocaust, imagine Jewish signmakers in the late 1930s going gangbusters with signage orders for "train stations" and "work camps", and then ending up in them.