Why has Islam forbidden Muslims to imitate others?

The Islamic Sharia prohibits Muslims from imitating disbelievers, based on the Prophet's (peace be upon him) saying: "Whoever imitates a people is one of them." This prohibition has multiple wisdoms, among them: it is an objection to God's law, it indicates psychological weakness and defeat, and outward imitation is accompanied by inner love and loyalty which are forbidden by Sharia. Furthermore, outward imitation leads to inward imitation in belief and doctrines.