(Original post by zhog)
Look, do you know what the first man-made construction visible from space is? This 'walls don't work' line originates entirely from people engaged in an effort to prevent one from being built at all. It's a line from people interested in facilitating illegal immigration, it's not as if they don't work to some extent in terms of deterring it. Ask Israel.
Actually, the story that the Great Wall of China can been seen from space is a myth. You can't actually see it.
A wall works in Israel because they have the manpower to patrol it constantly, because they have top-of-the-line surveillance and monitoring equipment to help the guards, and because the border is relatively small in length.
On the other hand, the US-Mexico border is over 3 million miles long, and covers rivers and villages. Monitoring and patrolling that wall constantly would be a near impossible task in terms of provision manpower and surveillance equipment.
And as many people have already said, people can just dig under the wall, especially if the wall is not being monitored properly. Cartels have been doing this already for God knows how long.
The southern border is not the largest method of illegal immigration into the US. The majority of illegal immigrants enter the country legally, and overstay their visas. A wall will not fix that.