Well, given the Left's penchant for violence (John Kerry's admitted war crimes; their gleeful support of murdering children; Ted Kennedy's
L'Affaire Chappaquiddick; Pete Stark's demented attacks and threats; the "mulch-assault" committed by Wanda Baucus recently; the anti-Semitic murders instigated by Al Sharpton; the murder of 55,000 Americans in Vietnam and 87 more in Waco; etc.), and their treasonous statements over the past decades, and accelerating in rate and viciousness in recent months/years, I think its only wise that the Secret Service take such precautions.
Besides, this isn't different than security for any other presidential visit in the post-Kennedy, post-Squeaky Fromme, post-Hinckley world. When Dwight Eisenhower visited Mount Vernon during his presidency he and two agents stood in line to visit the house. Sadly, our world is different now, and due in no small part to the coddling of criminals and the divisiveness perpretrated by the Left.