I can only speak for myself, but it's not hating people as individuals per se but rather as a collective society. It's more hating human nature than actual humans. I've come to believe that we humans don't have as much control over ourselves or self awareness as we would like to think, and that we are not much different from animals, as far as following instincts (a combination of individual instincts determined by DNA and life experiences and group instincts determined by location and society). Humans hate other humans they don't know. Humans are naturally judgmental (whether negatively judging people they don't know, which comes from a feeling of dislike or unfamiliarity, or even positively judging people they don't know, usually people who posses traits we find admirable and wish we had ourselves). My life experiences dealing with humans' cruelty and apathy (growing up in an abusive broken home, being treated like a labrat by uncaring doctors who destroyed what little health I had, to fill their pocketbooks and then throwing me to the wayside when there was nothing more they could do for me, and being bullied regularly by peers and complete strangers who despite not knowing me felt they had the right to treat me like garbage for their own amusement and having others either watch indifferently or blame me... all of this brought on a lot of hatred, but now I feel that it's pointless because it's nature, and not just humans either, but all living creatures. It's the natural order of things, although it's not as bothersome when animals do it because they don't put on charades about how they are, the way humans do, but again maybe that is also a human instinct). Being mistreated and hurt by both the people who are supposed to love and care for you and complete strangers a like can make you cynical of others and the human race as a whole. I guess it just comes from life experiences for the most part although reading through history and what humans have done since the beginning of time won't leave you with a positive view of humans or make you think that they are good for the planet.
To be honest the only living things that are the closest to selflessness on this earth are trees. They give life (oxygen, food, shelter, resources) to all creatures and get little in return.
I agree that humans are multifaceted but being a pessimist I feel the harm they cause this world overall outweighs the positive.
The above is just my opinion though, which is irrelevant in the grand scheme of things.