If a few minutes of reading TvTropes is anything to go by, the Tolkien never officially decided on an origin for his orcs. All of the possibilities he considered clashed with his legendarium somehow. And he had some of them that actively resisted Sauron, which makes them 'not strictly evil' I suppose.
You can't be evil if you don't have free will. A tool has no evil except from what comes from the hand that wields it. So to me, orcs make more sense as a constructed organic machine, little better than automatons, and with no moral sense of their own. A dog would have more capacity for evil. But the interesting question would ask who would have the capacity to create such machines, who believes that violence is an acceptable method of achieving their goals. You say that conscience is optional for antagonists? I'd say that a complete lack of empathy is the defining quality of evil, what drives them to seek power without any care for others.
Plus, having orcs lets you roll up a whole pile of mooks for your players to fight whenever you like, and if they happen to be trying to advance your BBEG's goal while completely indifferent to whether they cause pain and suffering along the way, all the better. Can't give the masterplan away if they were completely indifferent to why they were asked to do something and never asked questions about it, but it gives your players some goals to work towards and some puzzles to chew on.
And yeah, Strahd's entire backstory and motivation being 'he is a dick' is difficult to make interesting. A well-intentioned extremist that thought they needed power that they then could not control and which led them to darkness has the potential for some characterisation. Strahd wanted the booty but could not get the booty and is angry about it. Plus that module is just two hundred hours of one TPK after another.