Plus, apart from security concerns which can be dealt with other ways, JavaScript engines are now capable of running multiple web apps in many tabs simultaneously without being noticed. Wasn't performance one of the primary reasons for having this option back in the day? Now its not an issue. Going forward we might not see a disable js button and think it just as normal as not seeing an option to disable CSS or even html. It's kind of a non-optional piece of the web now.
Hardly. The number of people who chose to disable JavaScript is utterly dwarfed by the factors that get in the way of JavaScript successfully executing on the page.
Very simply: A browser can not execute JavaScript it hasn't received: http://isolani.co.uk/blog/javascript/DisablingJavaScriptAski...
You are reliant on factors outside of your control. For example, a well-intentioned DNS Blacklist took down loads of Fortune 500 companies: http://www.theregister.co.uk/2012/01/05/google_opendns_clash...
(I agree that the changing of existing settings is the offensive part.)