I think it's entirely wrong for Americans to sympathize with Boston victims while disregarding and in many cases outright denying the existence of victims of drone strikes. It's hypocrisy at its finest and especially rich coming from self-proclaimed Christians.
That is exactly the problem with nationalism.
I suspect you're probably saying that it's understandable for Americans only to feel the reality of this kind of cruelty when it affects "their own", and my response is that it may be understandable, but then so are the mechanisms of cancer.
We have social obligations first to those nearer us and later those further away. We owe our parents more than we owe strangers. If we are in a crowded theater and fire breaks out, we have a greater obligation to save our own kids' than our neighbor's, but we have a greater obligation to save our neighbor's kids than a stranger's. So obligations start at the family and household level and spread out in concentric circles of community. This is healthy and it is more or less the way humanity has always worked. The outer two levels might generally be classified as the ethnos and lastly everyone else.
Where I hesitate is where you say "in many cases outright denying the existence of" because that's a problem, but not because we owe no more to our own than to others.
The problem is also wider than mere denial of the existence of innocent drone strike victims, but this idea that because we believe we have justified reasons for engaging in drone strikes, everyone should just understand that. A healthier attitude would be to expect and value the fact that Yemenis and Pakistanis will value their family and community members more than Americans, and where too many people off base is that they don't expect or value that. They think the Pakistanis should be grateful that we are killing bad guys and that's where the problem lies. Attitudes like that make it impossible to build bridges between our peoples, to understand and respect eachother.
The alternative is to say that communities shouldn't matter. Why should the Pakistani not have American liberties? But then why should African Americans not be protected by European hate speech laws? Why should American Muslims not be protected against people insulting their religion?
In the end, I think that community (as a series of concentric circles) is important and as much governance needs to be as local as at all possible. This means tolerating all kinds of things we might believe are abuses of rights in our own culture while trusting that other people have the ability to make things work in a basically just way.
That is exactly the problem with nationalism.
I suspect you're probably saying that it's understandable for Americans only to feel the reality of this kind of cruelty when it affects "their own", and my response is that it may be understandable, but then so are the mechanisms of cancer.