It just occurred to me, but maybe in many fantasy settings crcs are considered evil because they are something akin to half animal half humanoid (pig snouts, tusks, etc...).
And by this, I mean their brains aren't fully developed on an evolutionary scale.
They still are connected to the primal and instinctive realms of animals, this can be shown in past editions (and even this one), by getting a -1 or -2 or -4 (depending on edition) to Intelligence.
Not saying there aren't any orcs that have grown to be smart, but it's a rare occurrence (in favor for Strength based builds) due to the minus they get to Intelligence.
Just imagine how many CCs (cubic centimeters) an orc brain has compared to a human.
On average, your modern day human has 1350 CCs of brain capacity, while an orc may have (if 10 is average Intelligence, an orcs get -2 to Intelligence, it means their average is 8)
So it appears that an orc on average will have 20% less brain power than a human, meaning they probably have 1080 CCs of brain capacity.
If you use the Intelligence score as a measure of IQ for the character (multiply score by 10, add result of 1d10 where 10 counts as 0 to determine IQ), it appears an orc on average would have 80-89 IQ.
With that type of average for intelligence, this being the top of the bell curve, an orc society is full of dull-minded individuals.
With a -2 to Intelligence that means their base score starts off at a 6 before being raised.
An orc with 7 Intelligence would have have some sort of borderline deficiency, while an orc with 6 Intelligence would be classified as retarded.
So with this reason, I feel orcs are more "evil" because they are still more primal in nature.
They have not evolved or developed a brain big enough for complex understanding (aside from an elite few), and it's easier for them to accomplish tasks through might (since they have genes that promote body growth) than it would be for them to figure it out.
In this sense, the orcs appear evil, when in fact they are less evolved as a species, and find an easier time raiding, pillaging, raping, murdering, etc...
P.S.
Their low IQs make them good for following orders and being general laborers.
Though complex tasks that require too much thought may anger them, causing the orcs to lash out in anger and destruction.