Having climbed ladders in the construction trades for the last forty years, I can assure you that most people will NOT just up and walk away from an 18 foot fall.
That's the height of an average two story house. A fall from that height will result in major, life changing injuries, if not death. A fall from less than half that height, can result in serious fractures and broken bones.
The people who fall from the 18 foot bollards are generally not standing on top, but rather hanging on with their hands. Their feet are more like 12 feet above the ground - several feet lower if they are defeated by anti-climb plates. Often the “fall” is a semi-controlled slide down the bollards.
The result is that it is rare that Border Patrol has to recover a broken body or medevac a jumper by helicopter. The thirty foot ones are a real monster though.
Kids like to climb on the 18 footers for fun, up to where the plates start. Without the plates, a typical (but daring) teenage boy can climb the 18 footers (they basically stop women and children). 30 footers deter most boys/men from trying. With a good anti-climb obstacle on top, 30 footers will effectively stop men.
True statement.