The question isn't Left Unity; it's determining which is the path forward for the party/movement, and do we work together in actions that some see as less than ideal (or outright hostile) from their perspectives, towards our common goals. Turning over Rosa to the government was, of course, a bad move; but with regards to the original split which facilitated the political conditions whereby that decision was made, did SPD have the political capital to resist the government's push towards war with the German working class? Could they reasonably expect similar support from the other socialist parties of Europe such that the war would be aborted before it began? Or did they assess, as their governments did, that slowing down or stopping mobilization would only lead to another Franco-Prussian war where one side got to the battlefield first and won without a contest (and all the known consequences thereafter, like the Paris Commune)? We know with hindsight that such intransigence against the government may have stopped the war in its tracts, or at least maintained moderate unity within the left, but we have the benefit of hindsight.

Basically, when is an issue non-reconcilable? We're human and prone to being biased and wrong, but even if both sides are "right" or internally consistent in their critique, it can still lead to splits. A bit of faith in our comrades, I'm sure, but too much faith and incomplete information can easily lead to an untimely death. I dunno, I got lots of questions and not a lot of answers.