As usual, my argument will be drawn from paraphrasing expert(s), but this time with simplified logic to prevent any circumvent of loopholes.
I will only be using one source this time. Though it is a journal of applied philosophy, the author employs economic journals as well to support his ideas.
The main argument here is that the transaction of the citizenship for goods/money is no different from regular transactions. If two parties would mutually benefit with no harm, then it is clearly logical to support this case. We have legal markets for good in general, so it seems illogical to abolish citizenship as a good if it is no different. Even though citizenship is not physical, it is a state issued right, just as your property is. Different countries give you different opportunities to lift yourself out of poverty. And so the institutional differences between developed and developing countries mean that immigration becomes much more beneficial. Through the better sufficiency and equality given in different countries, poor people may bridge the wage gap through the citizenship market.
The author counters five different arguments that may put doubt in this case.
Firstly, he highlights that citizenship is not an unalienable right (contrary to selling your liberty as slavery) -- many people already sacrifice their citizenship by moving from country to country for better opportunities. Thus Con cannot argue that you can't sacrifice citizenship. Secondly, he counters that selling citizenship would send the wrong message about using the rights as a means to an end. Even if undermining your citizenship was undesirable, it may be even worse for government to interfere in the transaction. Just as it may be bad for you to throw away your car keys, that doesn't mean government should force you to keep those car keys. It's your own job and your own private life to deal with. In fact, you could argue the opposite-- the fact that you are willing to buy citizenship shows a price and value. It replaces those who value citizenship less with those who value it more. So Con can't argue this either.
Thirdly, the author talks about potential exploitation that opponents are likely worried about. He realizes that if the state removes the ability to form a contract, this is contradictory since it further restricts an already limited choice set. You prevent the citizen from choosing an alternative he would have chosen above all others. Even if it becomes problematic for some population, so long as the general population isn't affected, the benefits still outweigh the detriments, especially if you enforce regulations. As the author suggests a solution, we may "enforce caps on the percentage of future income transferred in the ISA.34 By analogy, even if exploitative labourcontracts are impermissible, labour contracts generally may remain permissible."
Fourthly, the author tackles an argument concerning lack of true impact due to helping out a different portion of the population rather than the poor. Well, this also brings a flaw to the exploitation argument, as poor people would no longer be the major risk factor according to this logic. Furthermore, the two major requirements are that this argument justifies significant immigration restriction, and that the interests of those who don't move are harmed. It seems illogical that we would generally impose restrictions on someone's labor mobility merely because they gain human capital.
And the impoverishment of citizens has mixed evidence, especially since the labor movement *creates* a demand for it. Some people obtain skillsets precisely because they are able to move elsewhere, and therefore lack of citizenship markets would inevitably lose some important jobs that would otherwise be created. So the market would create incentive to gain more capital overall. The expert also suggests a plausible solution in general, with "condition that states tax the sale of citizenship and redistribute that revenuedirectly to remaining citizens or use it to fund various social programs". So even the small benefit overall could still lead to helping out the poor and a win-win situation.
Fifthly, the author fights egalitarianism. He admits that these markets can be unfair, but counters with the idea that citizenship in general is unfair. He notices that citizens in countries benefit simply by being/working in the country. He shows that "Migrantswho arrive in the United States, even those from the very poorest countries,typically earn close to what observably identical nonmigrants earn". He admits that open border policy would be the ideal solution, but in countries that can't afford the problems that occur (crime, smuggling, what have you), the markets would increase movement opportunities.
The author concludes by admitting there are not enough examples with citizenship markets in real life. But there are tangible benefits logically speaking, even if it becomes a niche market. The further experimentation allows for better statistics, building the foundation of better policies in the future.
If philosophy wasn't convincing enough, an economical article supports the overarching view of the author. As they highlight, immigration and naturalization in general helps wage gains, education, and that the social benefits are large, even if it's tricky to separate those who would've succeeded regardless. The substantial benefit to those in the labor market means that we must allow this market for citizenship. The catalyst for integration and the humanitarian mission means that governments ought to enforce it from a moral and economic standpoint. [https://wol.iza.org/articles/naturalization-and-citizenship-who-benefits/long
And so I affirm: this house would allow a global market for citizenship.