It probably won't be a facemurder effect unless you're in actively uttershit GM land. It will just be something minor, possibly even with no mechanical effects.To play devil's advocate a bit, there is something to be said for making it easier for those who don't have RPG instincts finely honed over a lifetime of ascetic training to identify when bad GMing is happening. Especially for someone who's the GM in question and has only half a clue what they're doing.
I can much more easily see someone genuinely honestly thinking "maybe requiring an activation roll on a Charm that does X would be a good idea" out of sheer naivete, and thereby accidentally screwing over the Charm, than genuinely honestly thinking "maybe I should let this facemurder effect bypass arbitrary defenses".
But while it is good to deal with that, doing it in a charm is the wrong place to do it. Dealing with OOC problems IC is a terrible idea, and trying to put things like that in the design by the developers is even worse.