One major problem is that if we start doing something like that on an extremely active basis we risk getting "retail tourist" SOs parking in eThailand to take advantage of our cheap-as-Hell currency to scoop up the bargain Food and donating it overseas, either for private consumption or for one of the active "Black Market" orgs.
The fact that there's nothing resembling export tariffs makes something of a mockery of certain aspects of eRepublik's economic system; e.g., the cheapest way to get raw materials from one country to another is by moving your company's owning SO to the producing country, buying the material, and then donating it directly to the consuming company. Viola: no import tax, no need for the supplier to buy an export license. One Moving Ticket and you can freely send an SO to pilfer another country's market.
[e] As to raising taxes on guns, it wouldn't work. The tax system is broken. They'd just drop their wages to the national minimum (currently 1 THB), pay salaries via donations to the workers, and remove their profits from the company untaxed by using company funds to buy out extremely overpriced offers from the owner on the monetary market. Since there's no export tax, nor are they selling the arms in eThailand, income tax is the only thing that applies, and as mentioned, that's easy enough to evade. The only other option would be to try setting up trade embargoes with every other country on the planet... and those, of course, are not product-specific, so it'd be total isolationism. Not to mention that arms producers have a noticeable presence in the Congress (and sympathizers w/in the administration), so there's no stomach for it. "Why punish our most industrious companies?" and such; this if we even talk about pushing their taxes up to 10% instead of leaving them at 5% like every other sector. Tragedy of the damned commons.