It is almost impossible to disagree with your statement.

I wonder if these numbers would have a better impact?
21.6 Billion Dollars to build a wall in three years (source DoHS)

16,200 migrants at border per month average.
583,000 if multiplied by 3 years. 

This means using an average of $39,000 USD to help 583,000 people in the most needed parts of Latin America and the Caribbean can have a much greater positive impact if done correctly.

Elon could easily partner with USAID and other private and public entities,
to come up with smart and humane alternatives rather that look for cheap attention to his social media platform.

There are endless industries that can see sustained and meaningful growth with micro-finance and training.