Why do we and Lego see the Trolls/Orcs as evil? A lot of reasons for this one. The obvious ones (influence of LOTR, DND, etc.) have already been covered so I'll look at the other ones:
Most of us on here, and in Lego, are American/European - 'Westerners'. Look at the Trolls - their primary weapon is the scimitar, and throughout history scimitars have been seen as an eastern weapon, so perhaps the Trolls seem more foreign and alien to us, and we distrust them more. I think Tolkien used this idea too:
Tolkien, describing things in Moria, wrote:Some of the swords were crooked: orc-scimitars with blackened blades.
Then maybe there's human instinct. Trolls and Orcs have always been shown as brown and/or green, and scaly/hard-skinned. Think of the green and brown reptiles of the world - crocodiles, alligators, certain snakes, komodo dragons. They're either dangerous to, or at least distrusted by, humans. I think our species has a natural dislike of scaly green creatures.
Lastly, the most obvious - Lego says they're evil
We've never seen trolls attacking any innocent civilians in a Lego set.
That's actually a good point - what have the Lego trolls done wrong? Read this from the Tower Raid description:
The knights have captured a troll warrior and locked him in the prison – but the other troll warriors are on the attack to get him back! The knights must use all their strength and skills to battle the rolling siege tower with its bridge and swinging dragon-headed battering ram.
Does anyone else think this makes the Crown Knights seem a bit evil? Sounds like they provoked the Trolls into attacking them.