Should Playwrights Direct Their Own Work?

I have recently been involved in two plays where the playwright was also the director. In one case, the person concerned felt that he would sooner have someone else direct his plays, but he didn't like to impose on anyone. In the other case, the person concerned felt that he was the best person for the job since he had such a clear vision of how the play should be performed. Also, he could be on hand to do the inevitable rewrites as the rehearsals got under way. That person subsequently expressed amazement at how differently the lines were performed to how they had imagined them in the writing, even despite their own direction. In my view, once the writing is finished, a playwright should be prepared to sever all ties with his or her brainchild (except for the royalties) and let it fly on its own merits. Also, a director should be prepared to go with the written word and not expect to be able to rewrite the script according to his or her whims or those of the actors.