**1. Orcs are not "Bad Elves"**  

Tolkien never clarified the origin of Orcs, but many theories were proposed. The most accepted one is that Orcs were Elves captured and tortured into a "mockery of life" by Morgoth. Getting twisted to Orcs had little to do with an Elf's moral fiber.


**2. All of Eru's creations seem to have the ability to be evil if they choose to**

Tolkien's world has Eru, the One God. Eru created the Valar (a pantheon of lesser gods / greater angels), their attendant Maiar (lesser angels), Elves, Men, and Dwarves (by adoption). We even have examples of evil Valar (Morgoth), evil Maiar (Sauron and the various Balrogs among others), so even if the texts lacked evil Elves (which they don't), there is no reason intrinsic to the world-building why Elves could not be evil. There is nothing inherently "non-evil" in any of Eru's Children.


**3. Evil Elves in canon**

By the time of *the Hobbit* and *The Lord of the Rings*, very few Elves are left in Middle-Earth - most of them dead or sailed. But the account of earlier times, the *Silmarillion* gives us accounts of many Elves who did evil.

   **A. Feanor**: Once the greatest of the Noldor, he forged the first weapons for the Elves, led the first Kinslaying, where *he **and** his followers* massacred a whole bunch of defenseless Elves in the land without death just because they wouldn't give him their boats; stole those boats and then abandoned half of his followers to a dangerous and fatal foot journey over ice because he was jealous and suspicious of his half-brother.

   **B. Feanor's Seven Sons**: They may be said to have started out as 'just following orders' and tried to make things right for some time after Feanor's death, but they ultimately led two more massacres for their father's crusade. 

   **C. Eol**: An Elf who kidnapped and forced his wife to marry him, then when his wife Aredhel successfully managed to take her son and flee, he followed her to try to kill the  son (Aredhel fatally intervened)

   **D. Maeglin**: Eol's son, who fell in love with his cousin Idril (taboo among the Elves), jealously sold out their Kingdom to Morgoth for the promise of the Kingdom and girl. Note that he had been brought up by Idril's father as a prince and had great esteem in the Kingdom already. He was the only Elf in Tolkien's works to willingly and knowingly work for Morgoth.

And these are just the bad eggs of ONE single Elven family - the House of Finwe.

Tolkien's conceit when it comes to Elvish information is that most of what we know is information as known to / written by people affiliated with the House of Finwe. We don't have as extensive information about individuals when it comes to the Sindar or (any information when it comes to) the Nandor, Elves who never sailed off to see the Valar. We also don't get much information when it came to common/non-Royal Elves. 

While the political situation of Elves in Middle-Earth (not only did all the Elves we hear about know of the existence of gods, even amongst the Elves who did Evil, the majorly politically significant ones were all opposed to Morgoth) meant that we don't know of any Elves who worshiped Morgoth the way the Black Numenoreans did, we have no canonical reason to believe that individual elves could not be as capable of being evil as individual humans. The Feanorians and Maeglin, all had their followers who followed their leaders in their misdeeds.