Sorry I'm so late to the dance on this one... This was a good thread and Dr. Proof makes some good points but to me the question comes down to this:
As they say "the road to hell is paved with good intentions" All that Tobirama did he did with the safety of Konoha at heart but in the end his actions failed to achieve his goals. He was pragmatic, using the "tools" he had at his disposal, we could argue that he did the best he could and even that he managed to maintain the safety of Konoha for a while but ultimately he should also be held accountable for the long term results of his decisions... both the fourth and the third's deaths could be viewed as a direct result of rebellion against the decisions that he made...
Oh and Edo Tensei? A jutsu is just a tool, like a sword, how it is used or abused doesn't make it bad or good... Tobirama can't be held responsible for how others apply the technique that he created.
is it an affront to nature? Probably.
Should he have created it? Doesn't matter he did... If not him then someone else would have?