Carl,
HTMLarea has been removed from OpenACS, but replaced with RTE which just works better, so in OpenACS 5.2 we have a better option.
There is no way to turn off the rich text editor per user. I think you are asking for a way for the user to choose what editing interface they want.
In fact, OpenACS has a huge shortcoming in that there is no centralized way to store user preferences at all.
AFAIK HTMLarea or RTE should just disappear if your browser does not support it. Which browser are you using? I am suspecting Safari which incorrectly claims to support the rich text editing features. RTE (coming on OpenACS 5.2) correctly detects Safari and does not appear.