I wonder how many armchair commentators have actually walked around the white house in recent memory. It is a restricted street with respect to vehicles, but people can walk, and group, and protest, etc freely right there.
People are climbing on the wall/fence at any time of the day (or night IME). People are also always putting their hands through the fence to snap shots of the building clearly.
It would obviously be a fine balance between letting people get to the fence, stand there and assemble there, and manage the split-second change when someone would climb the fence. It literally is a two second variation and someone would have to intercept.
Which as I understand, they did...
"Joseph Caputo scaled the north fence line of the White House grounds at around 2:45 p.m. and was immediately apprehended, the Secret Service said in a statement. It did not provide further details about the suspect."
There is a balance of security versus making the place look like a high security compound. Not sure how much armchair commentary recognizes the balance. Im sure there would be complaints if a high fence with barbed wire or electrification were present...