I am tired of this sentiment. It is not necessarily incorrect to ascribe partial blame to someone just because they got the short end of the stick in some situation.
Being a victim does not automatically preclude one from being at fault. For example, if I jump off a cliff without a parachute, it is clearly reasonable to blame me despite the fact that I am definitively a victim of the situation.
In this case, it would be reasonable to ascribe some level of blame to both parties; we ascribe blame to the cartel for murdering people (and clearly most of the blame falls on them), and we also ascribe some measure of blame to the victim for failing to take proper precautions. This is not an affront to the victim's character or a trivialization of their death; it is a recognition of the fact that, with some more preparation, the situation could have turned out much better for the victim. It is important to address these failures so that we might learn from them in the future.
Edit: Downvoters, please comment. I am curious what you think about this. In particular, I am curious why it is never appropriate to ascribe blame to a victim of any sort.