Disadvantages to the wall:
-Inconveniencing people who live near the border or want to travel across the border
-Government using eminent domain to steal fellow citizens land in order to build the wall
-Paid for by wasting 20-40+ billion dollars worth of YOUR tax money (Assuming you live in the US), and taking money from the budgets of extremely important government areas like the EPA, Department of Education, etc
(None of which is coming from Mexico, that was a lie) (It's not coming from the CIA either)
-Destroying the habitats of hundreds of different species of animals, causing irreversible damage to the ecosystem and potentially leading to full-blown extinctions
-Not only taking money from extremely important government agencies, but also failing to distribute cash to try to take care of the actual problem: Overstaying visas
-Easily defeated in dozens of different ways: Going around, above, under, really anything except through the wall is a viable strategy to get past it.
-Won't be equipped with any sort of camera system, and no plans have been heard about having it patrolled the entire way 24/7 as would be necessary to stop people going over
-Plenty of room for sneaky corruption and money funneling to a company that has Donald's, or Donald's benefactors "interest" in mind
-Will make it significantly tougher for illegal immigrants wishing to leave the country to actually leave, meaning more illegal immigrants in the country at any given time
Pros:
+Has a slight chance of balancing out the number of illegal immigrants it kept inside the country, meaning we've spent 20-40+ billion dollars of taxpayer money for a net effect of zero
+A couple thousand construction jobs for the duration of his presidency, lowering unemployment by 0.00063% (Yes, I calculated it)