What stops people from digging a hole under the wall?
What stops people from blowing holes in the wall?
What stops People from buying a ladder to climb over the wall?
Let's take your logic one step further:
Why don't we just tear down all the prison walls?
What stops prisoners from digging a hole under the wall?
What stops prisoners from blowing holes in the wall?
What stops prisoners from buying a ladder to climb over the wall?
Access and security in a small confined location. If you think a wall will solve immigration issues you don't understand the issues. Democrats want border security too but we don't want to throw money on a wall that won't help enough to justify the expenses. The border isn't the length of a prison and Mexico has far more access to explosives than a prisoner does.
Absolutely nothing will stop truly determined people. Nothing.
What the wall will do however, is deeply effect local animal's migration routes, and cause some already dwindling populations to die off. It will be an environmental disaster.
Then - there is all that money, that SO is needed elsewhere, and could do so much real good ...
What do you expect? He's a real estate developer who thinks the only way to get somethings done/show you did something is to build something. And of course he knows it'll be called Trumps Wall, thats another selling point to him.
So thats all it'll do - make him think he did something.