Mecheon
Sacabambaspis
Orcs have been playable in D&D longer than I have been alive. Dozens upon dozens of people have played as orcs as anything raging from "Chill warrior" to "Very angry wizard". We have so, so, SO many examples of orcs having free will that its ridiculous. Hell, even the 'Oh Gruumsh won't let them' arguments are null and void because of the existence of Many Arrows in FR, which Gruumsh was against.It is entirely possible, and ridiculously simple, to say "Orcs are one of those innately evil species." Giving EVERYthing in a world a conscience and free-will is counter to the adversarial and heroic nature of the game...and, well, impractical to a setting's internal consistency, in addition to everything else.
Its possible to say it, but its also doesn't match up with the history of the game or make things more interesting.
Goblins do mischief, not necessarily evil. So there's plenty of reasons. Maybe you need a reagent but nowhere you can find sells it, so you've gotta go down, down to Goblin Town and deal with whatever they want to trade for it (which isn't going to be anything normal, but not anything you can't afford). Maybe the Queen of the Elves has kidnapped a human princeling against his will to serve as her concubine and you've gotta infiltrate the Royal Palace to get him back and avoid a diplomatic incident, so who better to get in than the sort-of-fey with a massive chip on their shoulder against elves to begin with?OF COURSE they are. It's what Goblins DO. Why? Oh right, because Goblins are EVIL. So, yeah, they are "engaged in Evil." If they weren't why would you be encountering them at all?