>are not offensive.
How exactly is "off the reservation" not offensive in the way that several commonly used idioms are now considered offensive, such as "that is retarded", "that is gay", "you Jewed the price down", "I got gypped"?
>are not offensive.
Right, literally nobody takes offense to "off the reservation" because you of course don't mean Native Americans. Are you seriously saying that slightly racist terms are only ever offensive in literal contexts?