Murder-suicide cases are perfect examples of following the Golden Rule. They truly believed that the world sucks or that there's a better life in heaven, so they decided to take others with them. Hitler also very much had a utopian vision.
"Not every metaphysician is violent, but every violent man is a metaphysician." - Decline of the West podcast
Utopias are naive visions that cause far more harm than good. Eve shares the fruit of the knowledge of good and evil with Adam. Sharing is caring... and you see where that leads... The Golden Rule is the root of all evil.
There is no absolute morality in survival situations either. In war torn places where saving your own child would lead to the death of other kids, what would you do? There are no real answers.
I understand the points you raised, sadly it is a "twisted" application of the "golden rule", which is the summary of the 7 Laws of God that includes "YOU MUST NOT KILL". So killing self or others are definitely NOT INCLUDED in the correct application of the rule.
Eve's sharing the fruit is also NOT included, because BEFORE the golden rule, there is another HALF, which is MOSTLY overlooked nowadays, that is HAVING GOD to worship alone. Which coincidentally requires someone WHO APPLIES the second half(golden rule) to OBEY GOD. Eve having disobeyed God already by eating the fruit, is actually DOING harm to his neighbor. THUS IT IS NOT A CORRECT application of the rule whatsoever.
Disobedience to God is the "root of all evil," until an anti-Christ like Paul, twisted the matter.
:)
You know the answers, it is only hard to accept them, sometimes.
You're assuming sufficiently complete information datasets and rationality of decision making.