"Wall can be defeated by a ladder so its useless" is not an argument. Guess what? Door to your home can be defeated by a paperclip but that does not mean that you should leave your door open when you leave your home.
Lets go back to reality and look at how barriers work. Back in 2015 Hungary was besieged by immigrants. They build a fence to deal with that.
August - 57k immigrants entered Hungary
September - 138k
October - 99k
*Fence was build*
November - 300 (not 300 thousand)
December - 270
Attempted border entries have fallen since the barrier was constructed. During the month of September 2015 there was a total number of 138,396 migrant entries, and within the first two weeks of November the average daily number of intercepted migrants decreased to only 15, which is a daily reduction of more than 4,500
https://en.wikipedia.org/wiki/Hungarian_border_barrier