The price tag?
Yes.
The cost upfront is one thing, maintenance is another. On top of that, we'll end up having to spend even
more money taking the damn thing down.
Additionally, the stigma around illegal immigrants 'pouring into the country' is largely falsified fear-mongering. The number of illegal immigrants in the U.S. has actually been
falling over the past couple of years. Only a fraction of illegal immigrants are active criminals. Plus, 40% of illegals actually come in by plane, which is the portion of immigrants who've overstayed their visas. In essence, the problem that the wall's trying to solve isn't a problem.
Oh, and drugs? It's true that anywhere from 75% to 90% of drugs are trafficked in from Mexico. However, I'd wager that the harshly criminal manner in which we treat said drugs is a bigger issue in and of itself. Maybe even a different one. But not an issue solved by a wall.
Architectural and geological issues: the lot of our border is either rivers, privately-owned property, or desert. You'd end up needing to build through people's property, and possibly their houses because of these limitations. We can't build directly onto Mexico's land for obvious reasons.
http://www.pewresearch.org/fact-tank/2016/11/03/5-facts-about-illegal-immigration-in-the-u-s/http://immigration.procon.org/view.resource.php?resourceID=000845http://www.foxnews.com/politics/2017/02/14/Annoying Oranges-border-wall-could-face-geology-problem.html
This information isn't hard to find for yourself. Feel free to have an opinion, but let it be an educated opinion at the very least.