There is some risk anywhere you go but the risk is not even for everyone.
In other words, it depends on where you go, when you do there and how. Generally, larger groups traveling together are safer. Even not part of the group, following hordes of other tourists will make it safer for you, and indeed there are hordes of tourists in Peru in all major sites and along the usual paths.
Peru significantly benefits from tourism and it is in their best interest to keep things safe. Along tourist areas, there is a strong presence of tourist police from morning to around sunset.
It is sad to hear this kind of news and when a group is being particularly targeted you have to be extra caution if that includes you. Anything that can make you seem excluded would help. I know Americans how sew Canadian flags to their bags to avoid anti-American sentiments in some locations.
You are also asking about Bolivia and Argentina in the same question and should point out that those are separate countries. Such issues are really different between them. Just a few months ago (Dec 2012-Jan 2013), I was in both Peru and Bolivia as well as Ecuador. There was some uprest in Bolivia but never did I feel in any danger. It was my first time there, while I have been 8 o 9 times to Peru, but it felt even safer. Ecuador on the other hand is much more dangerous at this time.