Tenured professors, particularly of EWD's stature, get a lot of license to say what they want. I can certainly a few of my instructors who were rather colorful in a variety of ways.
Dijkstra was obsessed with mathematical correctness and certainly knew it was pointless to pursue in human language speaking about complex topics. He wanted people to pay attention, and they did. I think it's a testament to the effectiveness of his writing, and proof that it was not merely inflammatory, that people still read him and debate his ideas today, when his ideas have as little mainstream acceptance as they ever had.