Taint of the Orc

As the Elves held themselves apart from the Godswar in their search for immortality, others sought to punish them for their hubris. Many elves were tainted leading to them birthing strange children. Fearing contagion those elves and their twisted children were banished to Darkwood. As the nature of the Taint was discovered the Elves turned against their Orc offspring driving them deeper and deeper into Darkwood and eventually to Val'Dorath.

The Taint seems to infest an elf that makes all children of that elf be born an Orc, regardless of the sex of the tainted parent. Some of the first elves that died to be reborn through the Well were those who were tainted to bear Orc children. The Elves see Orcs as an existential threat and treat them accordingly.