Ironically the Zombie Survival Guide addresses this scenario. If you do that, the crush of bodies from the waves behind those you kill, etc... eventually create a climbable stair-case of corpses.
Hey... I didn't say it made sense... just that someone has considered the counter-point.
People were saying the same thing regarding Glenn and Nicholas on the dumpster
"You are safe, just stab them all in the head until you've killed them all"
This isn't a video game where bodies just despawn after death. Killing all those walkers leaves a LOT of bodies. They probably wouldn't be able to get over Alexandria's walls that way, but it creates other problems as well, like the fact they wil bel surrounded by rotting corpses that they have to clear away, where numerous things could go wrong.
Not to mention "putting a knife on the end of a stick and poking down at them" isa very stupid idea. Yeah lets lean over the edge and put all of our weight into a stick, so when it gets stuck in one of the zombies, or when one of them grabs it, or one of them bumps into it and you get sent toppling over the edge.
It is wayyyy too risky, especially for chickenshit idiots like the Alexandrians who could get ambushed by zombies in a brightly lit and completely empty room.
