Disabling all scripts by default, enabling them only for the sites they need, is at least recommended practice for any internet user. I would even go so far to say that it is reckless and careless not to. There are some nice plugins to allow scripts selectively for chosen sites.
This means that you have to assume that first time visitors to your site will not allow any scripts in their browsers. Your site should thus be able to present a useful interface to gather information what it is about, without requiring the user to allow scripts.
In my opinion, JavaScript should only be used to provide additional functionality that goes beyond the simple display of information.
My behaviour is like this: when I stumble upon a site that just displays "You need to enable JavaScript", I instantly reevaluate my interest that led me there. In some cases, I will just close the tab.
