Quoted for truth!
True that would be fun to watch but people would complain and you will see mass protest about border patrol firing at drug smugglers and landmines to keep illegal aliens out.
I might be out of touch but is everyone in the US trying to keep illegal aliens from entering the US and stop taking jobs. Even though they are min. wage jobs and are not meant to be a career.
Problem is that how can the marines get back into Earth. You basically need the Essay or marine spaceship and wait for orders to be deployed to some country. Since you have to factor the weather to send marines to space and sometimes there are usually delays due to weather or storaging weapons and equipment and getting them in the battlefield quickly without being spotted by the enemy and shot down.