Oh, please. Israel has walls (er, fences) and they work. The Hungarians have just put up fences and they are working. If you go to Europe you will see myriad walled cities from centuries ago and they worked. It’s not a total solution as you point out. Remember: our enemies want in and it’s not because they want to make a living here. That’s why we need barriers.
A wall is only effective if someone is not allowed to be on the other side of it. As long as illegals can have anchor babies, and get drivers licenses, free healthcare and jobs your fence won’t stop them from coming. As long as we are handing out asylum to terrorists, a fence won’t do much to stop them either.
Government is always looking for something that they can appear to be doing instead of fixing the problems they made for us themselves. Everyone has been talking about this wall for years and it’s just your typical government “just do something it doesn’t matter if it works” solution.