That's a line of thinking that if you take such a position you should probably not take the role.

Alternative: if you are a banking government boss type of position and go work in the private sector, don't work for your 'opposition', instead use your skillset in an unrelated area. It's pretty silly that we have to spell this stuff out for those people or even make laws about it since it's to blatantly obviously unethical that you'd think that even they can see that.