If conservatives were as serious about their preferred economic principles as they claim, they would embrace more immigration--and not just high-skill immigration. Here's why:
1. Freemarket principles: Labor is a market. It's like any other market. In most areas of the economy, conservatives see the value of preventing government interventions. When it comes to immigration, though, conservatives loudly support severe government interventions in the labor market. This particular intervention includes fences and armed border patrol agents and all sorts of other money drains. The benefits of nonintervention in other markets exist in labor too.
2. No more nanny statism: Current immigration law involves government telling businesses they cannot hire certain kinds of people. Why is that the government's business? In other areas, conservatives recognize that employment should be seen as a mutually voluntary transaction between employers and employees. Why do conservatives abandon this principle when they tell employers they cannot hire immigrants (and expect employers to enforce immigration law)?
3. Wealth creation: It is a simple truth that we do not make ourselves wealthier by producing things at higher costs than necessary. Preventing immigration--including low-skill immigration--obliges us to overpay for labor that immigrants could do for less. It is a waste of resources. It's like banning construction firms from using power tools. Hiring immigrants to do jobs for which they have a comparative advantage frees up resources for other uses, expanding our wealth. Conservatives should abandon their belief that only high-skilled immigration is good for the economy.
4. Most conservative excuses for opposing freer immigration either are bogus or can be fixed as part of immigration reform. See, for example, this discussion.
There are many other reasons to support looser immigration restrictions, but the ones I mentioned should appeal to market-minded conservatives.