Reavers are humans turned hyper-aggressive by PAX, and who's to say there isn't a cure that could reverse it? I honestly would rather liken Reavers to the various HMHVV Infected because Reavers seem to be semi-feral while still being able to perform complex tasks like piloting starships, and some of the more feral Infected lose control over themselves after a while.
I do however agree that canon-wise, Shedim are Bad News™. Their motivations are largely unknown to us, but we know that collectively they all seem to want to kill any living being without exception. Ibn Eisa, the leader of the New Islamic Jihad, was a great example of a Master Shedim. Instead of a shambling corpse with a malevolent intelligence who is hellbent on wantonly murdering everything in its immediate surrounding like its lesser Shedim cousins, the Shedim possessing Ibn Eisa's decaying body literally turned the Islamic Unity Movement into a terrorist organization and unleashed a wave of terror throughout the Middle East. In short, Shedim are bad, and Master Shedim are bad on a scale that's hard to comprehend.
It's also worth pointing out that Shedim, and indeed any being with the Evanescence weakness, may not actually "die" in the traditional metahuman view when they reach 0 Essence. It is unknown, at least to us as players from a canon perspective, whether Shedim who succumb to Evanescence are actually destroyed or merely return to their own plane of existence. As Street Grimoire points out, "for [the] purposes of us on the prime material the two results are pretty much the same", but for the purposes of this discussion this could at least in part affect the motivation of Shedim. If they are merely returned to their home plane they are effectively immortal and "live" to fight another day, but if they are destroyed then they are effectively "just" struggling for survival.
I don't think the latter, if even remotely true, makes them any less evil from the point of view of metahumanity in general, though. They're still bodysnatching spirits with a penchant for murder who feed on the life force of other living beings, and they exude an aura that literally causes living organisms to decay under continued exposure. The fiction insinuate that they kill people not because they have to to survive, but because they want to, and for no logical reason that anyone in-setting knows of. That makes them pretty much wholly evil in my book.
A shark isn't considered "evil" by most rational beings if it chomps a surfer.
A shark that somehow gained sapience, managed to leave the ocean and move into a highly populated area, and that then started viciously killing and draining human beings would probably be considered both terrifying and quite evil by most people I know.
