People with disabilities prefer CSS because it allows them to trivally alter layout and visual presentation in a way that works for them. For example, some people have trouble seeing low-contrast presentations; they can insert their own CSS into a CSS-aware page to make any site readable.

Actually, they don't. Pixel-precise css layouts (and numerous css hacks) make client-side stylesheets a nice idea in theory mostly.

Secondly, the use of CSS for layout has lead to a lot of web designers pretty much neglecting the presentability of plain HTML. Open Slashcode in lynx and you'll see what I mean; three pages of (mostly) irrelevant links before you get to the articles themselves.
Keep in mind, an individual using a screen reader will have to read or listen to all of these links before getting to the content.

CSS, like all the layout tools for the web that preceded it, is something that needs to be applied with great care if usability is to be maintained.