Of course you are right, this is not offshoring. And IT is something that's easy to offshore for real.
However while the effect of competition will tend to lower wages in general regardless, importing more people can only decrease the wage relative to the median of everyone making less than the imported workers even non-IT workers, and certainly those in direct competition with imported workers lose wage bargaining power. As imported workers become naturalized, they dilute the power over the geographical area defining the nation represented by one vote. Also remittances overseas tend to devalue currency already held.
Those who benefit are the ones who hire the cheap labor, who are few. Attempts to claw back the benefits through taxation are met with threats to relocate to more tax friendly climes, which mirror threats to offshore if cheap labor isn't allowed to be imported from the world at large.
The economists are right that free trade in goods and labor is more efficient, and raises GDP, but so what if the benefits accrue only to a few while median wage falls?
And while highly skilled labor may typically earn more than the median wage, by easing wage pressure, they rob opportunities and rewards from those already in the country, who might otherwise fill those positions albeit less efficiently GDP wise.
What happens when it's cheaper to import already skilled foreigners than raise a child to competency, is that the child is never concieved, yet the overall population of the country increases, degrading the environment.
The US Census Bureau declared in 1890 that the US no longer had a frontier. The need for the US to accept immigration in order to preserve it's borders ended then. Since then, every immigrant has been given opportunity from a finite pie that is the inheritance that comes from being born in the US. It's time to stop giving away the inheritance of opportunity being born in the 'land of opportunity' represents.
If people in the US want children in their lives who have a chance to have it as good as they do, they can't force their yet to be concieved infants to compete with imported adults.
People should demand that their country protects them from physical and economic harm. If your country isn't protecting you from harm, then what good is it? A smaller GDP with less people is better than a larger one with more.