Yes, selfishness, jealousy, hypocrisy, and self-centeredness can be a part of human nature, but it is all there is? What about compassion, understanding, a belief in equality? I've lived all my adult life identifying as polyamorous, so I perhaps see things from another perspective. For many of us, knowing that our partners have the freedom to choose, the freedom to explore, increases the connection as equals. For us, gander/goose is the norm.
It seems that a vocal contingent are triggered by the possibility of "their women" exploring as much as they are. From my perspective, this cuck-phobia is just that, a fear. It takes a certain commitment and confidence to engage in ethical non-monogamy, a trust in the process and one's partner(s). Referencing my polyamory, my father once told me that the very thought of another man touching his wife made him sick to his stomach and he saw that as an indication of his love. At least he was monogamous as well, holding himself to the same standard.