Right - well, you have to think something is likely to be dangerous to you in some way before you start adding paranoid safety features. The people who built the internet are mostly in a mutually beneficial relationship with it - so no problem.

I don't pretend that building a system which you can deactivate helps other people if they want to deactivate it. A military robot might have an off switch that only the commander with the right private key could activate. If that commander wants to wipe out 90% of the humans on the planet, then his "off switch" won't help them. That is not a scenario which a deliberate "off switch" is intended to help with in the first place.