Such people did exist - the Left's mistake is in assuming that because the Book in question advocates a peaceful philosophy, all people who lived under its laws were paragons of pacifism. Most humans aren't very spiritual and thus let their egos and minds drive their decision-making, so it's no shock to see nominal Hindus, Buddhists, Muslims, or even Christians butchering each other, no matter what their Books call for.
Another Left's mistake is giving all the credit to Gandhi, when in reality the lion portion of credit belongs to the British Empire in this case. Hitler or Stalin would have Gandhi and his followers just simply disappear.