I'm not conflating them. I think collective blame is generally a bad thing in itself and it is the way of thinking that begets racist and tribal attitudes. It is also inaccurate.

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).

I think this illustrates why it is in fact about responsibility, and thinking about it as blame gets you in confusion.

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.