If Span sits then who hits leadoff? That is the problem.
Anthony Rendon or Jayson Werth.
Honestly, even if he isn't benched, he shouldn't hit leadoff. He doesn't take a lot of pitches, he isnt getting walks, and he doesn't hit for a high enough average to put his OBP at a leadoff level.
Quite frankly, McLouth is probably a better leadoff hitter if given equal playing time.