"Someone else will do evil if I don't agree to do evil so I might as well do evil myself" is a bullshit argument. And your point is directly addressed in the article:
By resigning publicly, I am saddened by the knowledge that I likely foreclose a future at the State Department. I had not initially planned a public resignation. Because my time at State had been so short — I was hired on a two-year contract — I did not think I mattered enough to announce my resignation publicly. However, when I started to tell colleagues of my decision to resign, the response I heard repeatedly was, “Please speak for us.”