The beauty of "plain text" web sites is that with any decent web browser you can either turn CSS off, load your own CSS or switch to reader mode.
Of all the problems created by web and UI design, this isn't one of them.
User stylesheets are even part of the standard. The fact that the most common (and maybe "oppressive") browser doesn't support them is itself a problem.
It’s a great way to empower users. A feature, not a ”problem”.
Usually, if a web page doesn't already have a CSS though, then it is already good and I won't need to add one.
I actually want the ability to have "privileged" CSS commands which can only be specified by the end user, including meta-CSS.