If the standards and regulations that goverend the raising and production of meat were the same across all nations, then I'd agree that the decision would be a purely nationalistic one.

When Brazil is burning down rainforests to raise cattle, there are good reasons to care where your beef is coming from.

What's wrong with preferring your nation (language, culture, geography - doesn't necessarily map 1:1 to countries) over others, while living in your nation?

I'd be more worried about people who place other nations above mine while living in mine.

There are many environmental and other moral reasons to prefer more-local food (and other products)