That statement of humans being the greatest thing ever is in the context of a thread complaining about people using essentialist arguments to portray humans as essentially evil and use that to support not trying to change our situation. By saying humans are the greatest thing ever, you know I don't the person's exact intentions above, but by saying that one is countering these essentialist ideas and saying that no a better world is possible, humans can be better if we can just change material conditions, humans do not necessarily need to act the way we do under capitalism. Maybe humans are not literally the greatest thing ever, but it is a statement portraying humans as Subjects who are able to shape history. By going the opposite way and concluding that, no, humans actually do suck, you are precluding even the possibility of a better world, and any possibility that humans could act in any way different from today. It is a fatalistic position which precludes any action. I mean, yeah, recognize that humans have the capacity for evil and to suck and we're not perfect, but don't condemn us as mistakes who can never do better.