What would an Orthodox Jew do if a Messianic Jew visited their Synagogue?

What would a Christian (any denomination, take your pick) do if a devil-worshiping Christian visited their church? Would they be welcomed as a fellow Christian or would the congregation be a little uneasy welcoming someone who insists they are a Christian but who, because of their beliefs, obviously is not. Wouldn't the members of the congregation think this person was mentally disturbed? Answer honestly please.