If however you are a functioning member of a society and do things to support it you are partially to blame for the things that society does. That amount of blame is not the same for everyone - and for some people it is so minimal it hardly warrants mentioning - but you do have a share.
on edit: as an example we can say with some surety that the one white man in 1800s American that should not be charged with culpability for slavery would be John Brown (although he probably would not feel the same way) - there are undoubtedly others but we can point with some justification at John Brown and say that guy pretty much not to blame for any of that shit.
I'm certainly not recommending that people have to do these things either, just to being clear eyed about things - you can't benefit from your society's actions and then say you don't share any blame from what it does without some extreme dropping out of the system.
I mean, I can see where you're coming from. But at this point we are really at the fringes of culpability and it's more of an issue of semantics and definitions.
so yes, each of those 1.3 billion probably have an atom of culpability, so minimal it hardly warrants mentioning.
I'm a citizen of Denmark, I have some share of culpability in the wrongs my country does - I do a little to minimize those wrongs (when I see them) by voting against the perpetrators but that's about it - I support the country and it is partly my fault because I am too comfortable to do what would be required to completely absolve myself of any culpability because hey, I'm pretty okay (as most people throughout history have said)
Collective punishment refers to the punishment communities en masse for the actions of individuals, that may be being harbored by some members of that community.
Just because something is done in a collective manner does not absolve the members of that collective from the outcome.
Bernie Sanders is an American who was advocating against the Iraq War. He was clearly not culpable for it, and his causal role was to lower the probability that it would go ahead. This is an example of why it would then be wrong to blame "Americans" as a collective for the Iraq War. Bernie Sanders, a member of that collective, deserves either zero blame or negative blame (if that even exists).
To extend your example: Bernie Sanders as a citizen, and further a politician, acquires an amount of the collective responsibility for the countries actions in the Iraq War. Bernie Sanders as an activist has more than discharged that responsibility by actively countering it.
A citizen who has done nothing to mitigate or counter the actions is left only with the share of collective responsibility; however large or small that may be, it's real.