Emotions seem to have opposites because they reflect the levels of the neuro transmitters, which change over a continuum. Love becomes hate as the level drops, sad to happy, confident to fearful, pain to comfort, hope to defeat, envy to pride, greatness to meekness, energy to slothfulness, playful to serious etc. Combinations of the base emotions form the many shades. Envy is lust mixed with anger and meekness, or whatever. Your perception of anger etc. is very similar to other people s perception of it.
People look different but it is only skin deep.
People all have the same basic bone structure, brain structure etc. Size, strength, effectiveness may vary, but essence varies little. Our perception is skewed to maximize the differences. To an alien, we would seem as homogenous as lab mice. People of unusual races look similar because you have not had time to zero in on the small differences.