I'm from Argentina, and yes, you might find a couple of people who could be harsh on you if they find out you're English, they're fanatics, just like you might find enywhere else, but I don't consider they represent the majority.
I don't think you should find any problem, anyways, if you're asked for your opinion, I would just agree with what everyone thinks here and let it go, I mean, why would you say something you know locals would find offensive? It would be like telling an Israeli that you're pro Palestinian, it would just bring trouble and none of the two parties would agree, after all you're on vacation and just trying to have fun, why bring politics into the table? It's always a lose-lose anywhere in the world.
In terms of security, I live in BA, it's not safe, and it's not unsafe either, just like every big city, you've got to beware of pick pockets, specially in crowded places and subways. And you should avoid uncrowded streets during the night.
Hope that helps, best of luck!