Well, first off, the Orc does get the chance to resist the spell.
And even if he fails the RR, the most that the spell will do is make the Orc think that the Caster is a good friend, not anybody else. If the Orc would distrust, and/or attack the Caster's friends normally, he would still do so while under the effects of the spell (but he would not attack the caster - his good and dear friend).
And the moment that the caster tried to attack him, that would break the spell and the Orc would be able to act normally.
