You gotta remember, though, that Starfleet Doctors still honor the "do no harm" tenet. If Crusher allowed Worf to basically commit suicide, she would be ignoring her duty as a doctor, and her oath.
It could be argued that *refusing* to allow Worf to commit ritual suicide would be harm, since it's ingrained in his culture that this must always be allowed when a warrior can no longer fight. Forcing him to be kept alive against his will would be a much greater harm than a quick and honorable death.