Hi,
We have discussed this issue quite up front actually - and decided to follow our usual path. Wiki Loves Monuments is based on what countries recognize as monuments - in this case the national heritage board of Argentina. We don't want to selectively shop in such a list, as that would be original research - which isn't allowed per Wikipedia policies.
If the UK would have participated, that would simply have resulted in two sets of monuments on these islands. One set as recognized by the Argentina government, and one set as recognized by the UK government (if there are monuments there recognized by the UK). There are some more examples like this: Argentina also recognized some monuments in Antarctica and some countries have recognized monuments in former colonies, or they have recognized buildings that have been moved to another country over time (i.e. taken apart and reconstructed elsewhere, or shipwrecks).
Anyway, we don't want to take a political approach here but I don't exclude the possibility that this is taking an interest in Latin American media at some point. I suggest that then the explanation as above could be used to explain that it's about the neutrality principles of Wikipedia - and not about taking a political stance.
Lodewijk