It is, but there is a difference between narrow net cost to specific programs and overall economic impact, which the CBO did not pretend to assess.

The overall economic impact is quite difficult to access. I don't see any good sources for this. Even if the economic impact is positive(which many(majority?) of the economists say), it is difficult to quantify the social costs, more diverse societies do face many challenges.

Why?

Visa requirements.

Awesome. If that's the cost-effective solution, why not just do that?

Because both of the problem need to be solved. The majority of people come through crossing the border.

Sure! And perhaps there was a decent ROI on the fencing act of 2006. The economics are quite a bit different from a massive, expensive, minimally policed wall in the middle of nowhere built on mountains and wetlands.

Let's hope that Trump doesn't insist on a full border wall. I don't know what the current talking point is regarding this.