The wall came down due to economic reasons; not because it failed.
It is the attitude of the government in that once you reach American soil; you get certain rights and benefits until shown otherwise.
As a result; this buys the illegals enough breathing room that the bleeding heart illegal advocates can then marshal resources to con/delay the system until the illegals are able to get lost/forgotten.
When the illegals get to go to the head of the line vs people that apply through legal means it demonstrates a serious flaw in the system and priorities.
The wall failed because ultimately walls fail. A lot of Germans still made it over that wall. And does anybody trust a wall that was built to keep people out cant be turned to keep people in?
You are making a great argument for a more simple legalization process. One where illegals become citizens and are on the same playing field as legal citizens.