"In Faretta v. California, 422 U.S. 806 (1975), the Supreme Court held that the Sixth Amendment provides a constitutional right to a criminal defendant to decline the assistance of counsel and instead to represent himself. The Court explained that a defendant's decision to invoke this right should be honored even in instances in which a defendant would be better served with representation by counsel. The National Association of Criminal Defense Lawyers (NACDL) agrees, and believes that a defendant's decision to waive the assistance of counsel should be overridden only in very rare circumstances.
NACDL believes that Indiana v. Edwards presents such an occasion. The question presented in that case is whether and when a court can, over a mentally-infirm criminal defendant’s objection, override the defendant’s decision to represent himself and require defendant to receive assistance of counsel. Where the mentally-infirm defendant is competent to stand trial because, under the well-known formulation of Dusky v. United States, 362 U.S. 402 (1960), he can "assist counsel," but his mental abilities do not permit him to competently represent himself, NACDL believes that fair trial rights must trump the defendant's right to refuse counsel.
Ideally, however, this conflict between representational and due process rights would not arise in the first place. In the law of competency as it existed at common law and until 1960, courts asked whether self-represented individuals were competent to represent themselves, not whether they were competent to assist a non-existent lawyer. The question whether counsel can be forced on someone like Mr. Edwards would never have arisen because, without an attorney, he would not have been deemed competent to stand trial in the first place.
In the Edwards case, NACDL submitted an amicus brief arguing that the Court should eliminate the Dusky competency standard’s assumption that counsel is present and refocus the test on the ability of the defendant to present a defense, with the presence of counsel – only in those cases where counsel is present – one factor to be considered. This return to the common law standard respects both the due process right to be tried only if competent and the Sixth Amendment right to choose whether or not to waive counsel."
http://jurist.law.pitt.edu/hotline/2008/04/fair-trial-rights-must-trump-right-to.php