The Taser is just the latest in a long line of less lethal weapons to be used by the police, sometimes questionably. In the old days they'd use a lead shot sap or a pipe wrapped in newspaper so that they didn't leave marks, but that's old school now. I would argue that temporary electrical shock is preferable to a blow to the head, though both should be avoided if at all possible. If anything, the Taser forces more accountability, as there is always a record of it having been fired, and if I remember correctly in addition to the darts it launches confetti in order to mark the position of the officer when the device was fired.
Considering the lack of information in the article, I wouldn't feel comfortable second guessing the officer, naked or not I know that the mentally ill can be highly threatening, and exactly what led up to the tasing is not described. It may have come down to hitting him or using the Taser, and as said, the Taser may actually be the safer option.
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“The totally convinced and the totally stupid have too much in common for the resemblance to be accidental.”
-- Robert Anton Wilson