Here’s why:
1. Building it creates mighty bad eminent domain problems.
2. It is disliked by many border area Americans who depend on Mexican labor crossing over daily.
3. The Hispanics middle class is ever bigger, ever richer, and more politically vocal. (The number of Hispanics earning over $100,000 grew by 64% between 2000 and 2005, compared with 40% for all other groups on average.)