You give two reasons as arguments for your perspective of this debate. One was morale and the other was overall economic benefit. In reading Michael Clemens paper much is unknown concerning the impact to the receiving country depending on the skill-set of the immigrant and the country where the emigration occurs. Some of the remedies proposed further complicate the picture so for expediency I would like to limit the scope of this debate to the specific US Policy of open immigration and its impact on US citizenry. I believe immigration policy is a social policy. And social policy is by definition class based. I will take the class analysis behind these statements for granted moving forward.
I would like to start off by saying that my morale rationale is overridden by concern for my own personal well-being and that of the people I personally know, love and respect. As a logical actor in this debate I am not going to support a policy that I believe will negatively impact me or anyone I associate with. To be more specific the socio-economic class with which I belong and the ones I sympathize with. In addition if we really want to discuss inequality throughout the whole entire world, the entire policy stance of this country would need to change because there are a host of policy’s our country pursues that are exponentially more blatantly morally wrong then our immigration policy. Thus I cannot in good conscience support a policy such as this on moral grounds unless there was a wholesale change in US policy that similarly negatively impacts US corporate interest on a wider scale.
Now on to your economic argument. I do not believe that everyone will be worse off or conversely better off if this policy were to be implemented. I believe there will be both winners and losers. For sure corporate interests stand to benefit immensely from something like this. I believe the wealthy and those at the higher end of the socio-economic scale will on net probably benefit. However, those on the margins of our society will assuredly lose. I do agree with the research that shows that US GDP would probably see a marked increase however those GDP gains will mostly accrue to the owners and managers ie. (Capital) in our economic system and not the masses ie. (Labor). For context, real wages in this country have been stagnant and declining for decades while GDP has continued to grow and this is for both blue collar and white-collar workers. I think the largest logical leap you make is when you assume gains in GDP equal gains for all. An illuminating paper describing our current economic challenges in detail was written by Lawrence Mishel and Heidi Shierholz. This distinction, between capital & labor is at the heart of this debate and my point. Corporate profits are currently at record highs but the rewards for these profits are not being shared widely. To increase the supply of labor when wages have been in continued stagnation and outright decline doesn’t seem like the recipe to produce a turnaround in that outcome. Bryan Caplan references this fact when he acknowledges the research that shows wages would decline.
In summary, I too don’t see immigration restrictions being the barrier to Americans wanting to start a business in Haiti, its capital and that is mostly controlled by large multi-national corporations and not the working class. I think you are correct when you observe that the argument against is motivated by concerns that things will be worse. I just think you don’t appreciate who it would be worse for. It does not makes sense to pursue a policy that intuitively and qualitatively impacts the class of citizens that are already struggling for a share of our countries prosperity.