I agree that web pages shouldn't have executable code. I think that's a separate issue from whether or not, given that web pages already have it, javascript is a reasonable choice. It's also a separate issue from whether or not live-editing ASTs for rich text is an appropriate GUI layer for javascript.

Basically, to the extent that web tech is acceptable at all, it has no interactivity. HTML and CSS aren't particularly good even as representations of static rich text, but they are far, far worse as graphics toolkits.