Duncan, you are quite educated and informed and I feel honored to be bested by you in debate, Sir.

We currently accept some 300,000 legal each year! Perhaps a solution would be to increase that number.
It is estimated that some 500,000 illegally cross each year!

So if we increase the "quota" to 800,000 or even 1,000,000 might that not be a way to correct the problem.
It seems so simple, yet I'm sure it isn't. I am completely ignorant of who sets these quotas and how they are determined, and why the number 300,000 is chosen, for example.