If all the people of Earth decided that resolving their differences through violence and war of any kind was unacceptable, and formalized their agreement on this one stance through a treaty, does that automatically make the treaty binding on extraterrestrials?
No, an enforced Kellogg-Briand treaty interpreted that way would constitute a suicide pact in practice. No constitution or treaty can be legitimately be interpreted as demanding suicide.
I don't really think there will be an end run around relativity cheap enough for space war. Thus it appeared to me that the argument that surrender of war as an instrument of policy is equivalent to surrendering the right to live, is meant to imply that a principle of sovereignty, the right to wage war, must be preserved. With the further implication that given war, a disunited is the only free Earth. Sorry if I read too much into this.