Actually, this episode highlights two sorts of stupidity. First, it shows that a fence is most likely ineffective in the first place, whether single or double. The time required to build an "earthen dirt berm" of the size required to accomplish their tactics was not insignificant: it took hours or even days.
Second, however, despite their obviously enterprising attitude, the stupidity of the smugglers cannot be overstated. If they've got earth-movers big enough to build this berm in a timely manner, why not just use them to drive through the fence?
On second thought, perhaps the smugglers weren't so stupid after all. Nothing better than an eye-catching display like this to distract attention from the real crossing point....
The smugglers know, after all, that it's a lot easier for them to pick their crossing spots, than for the Border Patrol to handle them.
Fencing cannot be 100% effective, but it is a significant improvement. The builders of the 'better mousetrap' have to be people of significant means. If the fence isn't 100% effective at stopping drug smugglers, it's pretty good at slowing them and probably really effective at stopping jumpers(especially those with families in tow.)
If we wanted to cripple the Mexican drug cartels, we'd have to cut their main source of funds. That would mean decriminalizing and regulating marijuana.