Require Javascript on site?

[Vanilla]

Well, i know that a lot of javascript might be used unnecessarily, and might not be needed, but the same actually goes for CSS in a lesser degree, if you look at the broader perspective. I mean, when you lay down the cards, CSS is only used to enhance your experience with the site, and so is Javascript (if used right). You could potentially view a plain html site just fine with just text. The internet is just there for people to share and get information. But today, it's almost a non-arguable standard that you have CSS activated within your browser, because otherwise your site would look like sh*t :P. Both Javascript and CSS is there only to present a website in enhanced visual manner.

Another side of the case is Javascript vs. Flash. Until recently, Flash's only rival was Online Java applets, but due to the speed and difficulty write such application for online use, Flash claimed tremendous market share regarding interactive online media. HTML 5 and it's enhanced javascript features (Audio, Video, 2D-drawing and also 3D with Googles O3D) is becoming a much more interesting solution with it's versatility, seen in contrast to the Adobe Flash Player. The could potentially make javascript a much larger player in the future.

Also, considering that top-100 sites such as Youtube and Facebook relies heavily on javascript, and deactivating it would degrade the experience to a very high degree, and in Youtubes case you can't even watch videos without Javascript, thus it requires you to have javascript in order to make use of the site.

So again, can I require Javascript on my "casual" site? Does it matter what kind of site it is, and what content is has? And in that case, on which sites is it acceptable to require javascript to actively make use of the site?