Now that I'm actually looking into it, I'll just drop this post off I've seen from reddit and move on. It has some points that I didn't even realize....
Look, I understand how a wall seems like a common-sense solution if your goal is to keep people out. If you're one of those people who thinks there is some sort of immigration crisis wherein we're being "flooded by illegals" (we're not, by the way; we've been
experiencing an outflow of illegal immigrants since around 2009), I can see how that option might be attractive in it's simplicity.
The problem is, it's simply a rediculous idea.
First, I haven't seen any credible estimates that suggest the wall will be a net positive boost to the economy. I know of the CIS study that came out, I've read the rebuttles, and the rebuttles of the rebuttles, and one thing is abundantly clear: that study is deeply flawed and cherry-picked. Being that it would be one of the most expensive pieces of infastructure ever built, I would need some seriously bullet-proof numbers before I would want any of my tax dollars to go to it. And if you're truly a conservative, and can honestly say you're in the "fiscal responsibility" camp, you should view it with at least the same amount of scepticism.
Second, border crossings themselves are at an all-time low, something Trump himself
loves to talk about. Putting aside the rhetoric (since this trend also predates Trump's presidency by years), you might be tempted to think, "well sure, we're protecting our border better and a wall will only help!"
When in fact, this is likely due to a great many variables that have little to do with border security, such as the fact that Mexico's economy is actually doing pretty well, and
their fertility rates have been falling steadily, alleviating demographic pressure to migrate(WARNING: PDF download).
Another reason a wall won't work is that the vast majority of illegal immigrants are a product of visa overstays, making up
over 40% of illegal immigrants. A wall won't keep those people out.
In regards to my previous point, I've seen it argued that of course you should do something about visa overstays AND build the wall to address the issue on multiple front. While that's a fair point, I believe it's myopic. Which brings me to my next point.
The solution to illegal immigration may actually be...less security.
See, from 1965 to 1985, around 86% of undocumented entries were offset by departures- meaning it was mostly cyclical This was back when border security was minimal, and crossing back and forth was fairly simple. Then, Reagan decided to militarize the border, inflating the cost, in terms of both money and danger, in crossing the border.
It used to be that immigrants would come to the US for a few months, work for a bit, and then cross back. In the mid eighties, we poured millions into border security, but caused the immigrant population to explode, because those migrants were now stuck here, unable or unwilling to make the now expensive and dangerous trek back home. This militarization was continued and increased throughout the Clinton and Bush administrations as well, and came with an even larger increase in undocumented immigrant populations.
Doug Massey, who runs the largest and most comprehensive database of US migration statistics in the world and author of that last source I posted, estimates that by opening our borders back up, we would lower net migration by a third. No wall necessary.