If a D/ST gets credit for a special teams touchdown (i.e. kickoff return), then D/ST should get negative points (i.e. points against total) when a fumble occurs on that special teams play and is returned for a touchdown by the opponent. Simply awarding a D/ST for touchdowns is counterintuitive and rewards teams who are reckless in their special teams plays.
Thanks for your feedback.
Items that count towards points allowed are all TDs scored against the defense or special teams from fake punts, field goals, returns from kickoffs/punts/blocked punts.
A TD return from an interception, fumble or blocked field goal does not count. In the case where two special teams are on the field and a fumble recovery was returned for a TD by the opposing team, it is perceived as a defensive scoring play, thus not counting against the other defense/special teams.