...in computer security.

Here I thought the dumbest idea in computer security was changing user passwords every 30 days.

The last useful thing Marcus Ranum has done for the
computer security was the fwtk 1.3 release.

Ability to execute arbitrary programs is what makes
a universal computer useful. Without that it would
be another embedded chip.

From the linked site: "It is often easier to not do something dumb than it is to do something smart."

This sounds like it could be phrased as a corollary to "It's better to remain silent and be thought a fool, (etc.)"

Such as, "It's better to wait a moment and be thought timid, than to act without thinking and be proved stupid."

Ability to execute arbitrary programs is what makes a universal computer useful.

Of course it is, but that wasn't what he was talking about, which was executing arbitrary programs without specific permission. Big difference.