Oracle gripe

For as much money that gets spent on Oracle to run our databases, why do we have to spend so much time telling Oracle how to return the results? Drop some changes to the database and suddenly certain queries are dog slow. The DBA has to spend valuable time hinting his way out of the query to get it to perform. Shouldn't this be the job of the DATABASE? I shouldn't have to tell the database to use a certain index since it may speed up the query results. Shouldn't Oracle prefer to use the index to doing a TABLE SCAN? I find this shocking, but it also appears that the Oracle DBA's seem to accept this as standard operating procedure.

My goal in using a database is to say "I want these rows from these tables that meet these conditions. Figure it out." Not "I want these rows from these tables using these conditions and, oh, use this index here and that one there. (Hint, hint)."