Oh, I see what you're saying and can see that happening and being set up now.Christians won't really be terrorists....they'll merely be presented in that way in order to discredit them. Many (hopefully all) Christians won't take the mark in those days, and there will be some who will need help in one way or another. In order to prevent the marked citizens from helping the unmarked, it will be declared that Christians are responsible for all the evil doings that are occurring and therefore should be turned in.
I still am not convinced this is a literal outward mark though.