As an alternative option you might wanna use ValidateInput as described here. An example in MVC style would be:
[ValidateInput(false)]
public ActionResult Method(){
return View()
}
[ValidateInput(false)]
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Method(){
// your stuff here
RedirectToAction("index"); // or something
}
I think that is more the MVC way to go. Now your controller tells you there is a security issue in that controller method. Your view can be any normal view using html helpers etc. Note that this enables all sorts of input, not filtered. It will work with TinyMCE though.
//edit
woops I see you need to add
<httpRuntime requestValidationMode="2.0"/>
to webconfig as well in new versions of MVC. Guess it might not be the way to go.