Back in the times when I read that statement, it had immediately lost credibility to me. The argument was basically an appeal-to-authority/argument from authority. It put Tanenbaum onto the "villain" side in my mind, someone who was willing to use his position of authority to win argument rather than merits. Subsequent strings of microkernel failures proved the point. The moment Microsoft moved the graphic subsystem from user mode into the kernel mode to mitigate performance problem was the death of microkernel in Windows NT.