Washington, who initially used the epithet during an onset clash with a co-star, told Newsweek magazine that "someone heard the booming voice of a black man and got really scared and that was the beginning of the end for me."
He tried to make amends by expressing remorse and volunteering to enter a counseling program to understand how the confrontation got out of hand, he told Newsweek.
"My mistake was believing that I would get the support from my network and all of my cast mates across the board. My mistake was believing I could correct a wrong with honesty and sincerity," he said in the interview posted online Thursday.
"My mistake was thinking black people get second chances. I was wrong on all fronts," he said.
His unwillingness to act like a submissive black at work was part of the problem, Washington said.
"Well, it didn't help me on the set that I was a black man who wasn't a mush-mouth Negro walking around with his head in his hands all the time. I didn't speak like I'd just left the plantation and that can be a problem for people sometime," he said.
"I had a person in human resources tell me after this thing played out that `some people' were afraid of me around the studio. I asked her why, because I'm a 6-foot-1, black man with dark skin and who doesn't go around saying `Yessah, massa sir' and `No sir, massa' to everyone?
"It's nuts when your presence alone can just scare people, and that made me a prime candidate to take the heat in a dysfunctional family," he said.
ABC declined comment Thursday. In its one public statement regarding Washington, issued in January, the network said his actions were "unacceptable."
Washington, who used the slur against co-star T.R. Knight during a confrontation with Patrick Dempsey, repeated the word backstage at the Golden Globes in January in denying the first incident. A public apology to Knight and others followed.