The Prime Directive is not a bad idea when it exists to minimise harm.
When it gets turned into a pseudo-religious dogma, where it is considered better to allow a culture to be extinguished than to risk contaminating it, that's when there are problems for me.
Zero tolerance policies ensure injustice in outlier cases. Yes, it’s unethical to interfere in a civilization’s development 99.9% of the time, but there are always exceptions. Ignoring outliers is pretending your system is above the fundamental laws of the universe.
A thought experiment occurred to me. What is the absolute best subject for a zero tolerance policy? Genocide is the first thought. The most horrific evil that could ever be inflicted.
But let’s say hypothetically, there was a virus that was highly-transmissible and has a 100% fatality rate. A virus killing all of mankind. And let’s say somehow this virus is sentient. We have no idea how it works, but we can confirm that it thinks, feels, etc. The virus is provably sentient for our hypothetical purposes.
If someone develops an absolute cure to the disease, it will save everyone, but it will also wipe out the sentient virus. That is technically genocide, but it saves all life from death. Should a zero tolerance policy govern? Or can we at least have a conversation about wiping out the sentient virus?