You don't "march" to lobby, you march for the media exposure.
We're already getting tons of media exposure. In the past six months we've had front page articles in major newspapers about:

  • Don't Ask, Don't Tell
  • Defense of Marriage Act
  • Prop 8 in California
  • LGBT anger at Obama's inaction on gay issues
  • Barney Frank introducing ENDA in Congress
  • LGBT-inclusive hate crime legislation
  • Obama's Stonewall-commemoration reception in the White House
  • LGBT Democrats boycotting the DNC's gay fundraiser
  • Recognition of same-sex marriage in Iowa, Vermont, Main, and New Hampshire
  • An openly gay host (Neil Patrick Harris) of the Tony Awards
  • American Idol runner-up is rumored to be gay (and later comes out)
  • New openly gay member of Congress
  • NY about to pass gay marriage until their Senate implodes
  • Obama appoints openly gay head of personnel office
  • Two lesbians on the initial list of women being considered for Supreme Court seat
  • Delaware adds sexual orientation to their state non-discrimination act
  • Washington DC recognizes same-sex marriages from other states
  • Iceland becomes first country with openly gay head of state
  • India strikes down sodomy laws for New Delhi


This isn't even a complete list, either.

While the power of the media cannot be understated, we are already receiving massive coverage of our issues. The March on Washington in 1989 was to promote LGBT visibility. We have that now making it an insufficient reason to hold a march.

--Aaron

Edit: fixed grammatical error