I believe that the traveller has done bad things, but this doesn't mean it's necessarily evil, but just a bad reputation. Maybe it tries to help and just fails. Nevertheless, the darkness is still evil. Fallen- A race of scavengers and fight anything in its way. Hive- race of warshipers that will follow its leaders. Pure evil Vex- programmed to kill and careless. Cabal- an army on a conquest to capture many planets too expand life. So even if we do not agree with the traveller. To fight off the darkness, we need it just as much as it needs us.