Ludwig von Mises: "The productivity of social cooperation surpasses in every respect the sum total of the production of isolated individuals." - Epistemological Problems of Economics
There are some very compeling reasons for distinguishing between a non-interventionist and isolationist foreign policy. The key differances are over international trade and immigration. In sofar as isolationism applies to economics and the association of individuals, it is a bad thing and constitutes a form of interventionism, not non-interventionism. Economic protectionism is a key tenet of traditional isolationist foreign policy, as is what could be considered cultural protectionism. While the paleo-conservative movement can be considered better than the neo-conservative movement in various ways, unfortunately many paleoconservatives have a tendency to support protectionism.
What does the isolationist foreign policy imply? Painfully high tariffs, import quotas, export bans, immigration quotas, martial law at the borders, walls at the borders, prohibition of lower-end jobs, prohibition of various goods and services. Taken to it's furthest extremes, it implies a ban on all trade and immigration between America and other nations. In either case, it implies a plethora of potential government interventions. This sentiment represents a sub-culture of "buy American products only" and "the immigrants are taking our jobs" people. It has culminated in a "anti-globalization" movement, constituted by people ranging from the far left to the paleo right. This sentiment is riddled with economic fallacy.
The non-interventionist foreign (and domestic) policy, in contrast, would inevitably have to be opposed to such measures. They are, afterall, government interventions in the market. The non-interventionist foreign policy with respect to foreign trade can only lead to one possible conclusion: the unhampered division of labor, voluntary exchange, is the correct policy for both inner-national trade and inter-national trade. This inevitably means that protectionist devices such as tariffs, quotas and prohibitions have to be eliminated. If we accept the principle of the division of labor within a country, we must accept the division of labor within the world. "Globalization" is the beginning of the global division of labor.
For the same reason that blocking trade between people in New Mexico and Arizona would have a hampering effect on production, so too will blocking trade between people in, say, China and America. Economics provides us with the insight that voluntary exchange is mutually beneficial to both parties and has a ripple effect of sorts (I.E. its benefits may extend beyond the two people exchanging down the line). Any kind of protectionism is going to block this mutually beneficial exchange. It always is at the expense of consumer choice and bestows a privilege to one narrow interest at the expense of everyone else, and eventually at the expense of the original "beneficiaries" themselves. And since it stifles competition, it has the obvious effect of artificially keeping prices higher than what the true market level would be. This has been proved beyond the shadow of a doubt in the field of economics long ago.
If mass-protectionism were instated on a world-wide scale, here is what would happen: first, people in 3rd world countries would die off like flies, secondly, 1st world countries would experience a restriction of supply (and thus bloated prices) and thirdly, the population of 1st world countries would also start to decline. In other words, it is impossible to sustain the global population without the expansion of the division of labor. Mass-protectionism creates the effect of a major restriction of access to resources for all parties. Such restriction can only lead to population control.
Let us examine the isolationist policy as it applies to immigration and questions of segregation vs. integration. The isolationist position on immigration is, at minimum, to greatly limit immigration. This involves a plethora of proposed government interventions: immigration quotas, going after those who hire immigrants, putting up physical barriers such as walls and fences, increases in police powers and persueing the drug war at the borders. Once again, the non-interventionist position must oppose such measures. But not only are they all government interventions, many of which are economic, but they violate very basic rights of both immigrants and citezens who associate with them.
Immigration itself is merely the act of moving from place A to place B. This is typically coupled with the act of purchasing a home. It should be obvious that this is a free trade activity just as much as any other. Yet many anti-immigration advocates, in effect, wish to illegalize selling goods and services to such people, hiring such people or allowing them onto one's own property; charity even. Such measures inevitably violate the property rights of both the immigrant and the ciitezens that they are associating with. If the government stops me from selling a home to an immigrant, hiring one or associating with them in any way, then my property rights are being violated along with that of the immigrant.
Libertarians are bound by the non-aggression axoim. This axoim leads one to support free association (and disassociation) between individuals on the basis that no aggression is used to force people to either associate or disassociate. This means that one must oppose both forced integration and forced segregation (forced association and force disassociation). If force is used to stop people from voluntarily associating, then a rights violation has occured. As such, using the law to stop immigrants from associating with citezens (and all that comes with it) is a rights violation on the part of both people in question. But the cultural isolationist essentially is argueing in favor of using the law to enforce forced segregation.
Of course, economically and socially, such separatism is counterproductive even for the people who wish to remain isolated. While people are perfectly within their rights to choose not to associate with people, they undermine their own well-being the more liberally that they isolate themselves. For example, if a buisiness refuses to sell products to group X, they lose buisiness, indeed, they are restricting their consumer base. It becomes vitally in the best interest of people to associate and engage in social cooperation, otherwise they harm themselves in the long-term by withdrawing from the benefits of society. This applies to immigration as well. To forcably block off immigration is also to aschew the benefits of social cooperation. While there is indeed a right of voluntary disassociation, the person who chooses to freely disassociate often does so at their own risk.
The non-interventionist policy towards immigration inevitably can only lead to the conclusion that immigration, free association and movement of people across land masses, must be left entirely alone and unhampered, within the domain of private property. The isolationist view sharply contrasts from this, putting forth that this free association must be hampered by the government in the name of preserving "the nation", "our jobs" or "our culture". The political isolationist is a separatist who wishes to use the state to enforce their desired separation. They are not content with free disassociation; they essentially want to make it the law that people must disassociate.
Simply put, the isolationist policy is a form of interventionism geared towards forced disassociation/forced segregation. The non-interventionist policy, as can obviously be inferred from the name, is the lack of interventionism, which can only lead to voluntary association and disassociation, and thus be in opposition to forced association and disassociation. The non-interventionist policy does not suggest wether to associate or disassociate, only that it be done voluntarily and that the government not intervene. On the other hand, the isolationist policy does indeed make a judgement and suggestion in favor of disassociation and supports force (governmental or otherwise) being used to bring it about. Isolationism is essentially a policy of government intervention to stop people from associating.