As we have seen, the new Anti-Xeno weapons are quite effective towards our Thargoid neighbors. My question is this, why don't we suffer the same ill effects when we come into contact with Guardian tech?
My best guess is a long standing theory regarding the possibility of Humans and Guardians being related, or at least similar in biological nature.
While yes, the missiles were tailor made to kill Thargoids and not humans; the question still stands. Why does this work? We know through various experiments performed by many of the minds at Cannon and elsewhere *cough Radio Sidewinder cough* that the Guardian tech has an extreme adverse effect on Thargoid tech. This suggests either a past where the two species fought or a possible 'allergy' of sorts.
Oh, it's quite possible humans are somehow related to the Guardians. Perhaps they genetically modified one of our ancestors to guide our evolution. They couldn't have clearly created homo sapiens as direct product, because the Guardians went extinct 1-2 million years ago and homo sapiens appeared around 250000 years ago.
As for why the Thargoids react violently to Guardian tech, and why the "Relics" were needed by Liz Ryder to make the AX missiles: that's just more evidence that the Thargoids are either the automated weapons systems left over from the Guardian civil war, or the evolved descendants of those weapon systems. I refer you to Guardian History Lore #20:
"20 – It appears that the Guardians approach to warfare vastly changed as the war continued.
Warfare was conducted using automated battle fleets. At first these were controlled by the Guardians via brain implants, but later they became entirely autonomous. In the early stages of the war the Guardians fought each other directly, but within a decade – and after much loss of life – most of the fighting was conducted remotely. Soldiers were deployed only to occupy areas that had been captured by autonomous or remote vehicles, and eventually were not used at all."
Combine that with the fact that we know they preferred to wage war with sophisticated bio-weapons:
"11 – Until now, Ram Tah did not know if the Guardians were using their
genetic and biological manipulation skills to develop their weapons and technologies. To those who claim that our technology is equal to the Guardians’ technologies, Ram Tah would say that integrating this technology to a societal level has given them a better knowledge of its application. They have developed creatures to use in combat… creatures that have remained very effective in the modern era.
12 – This data we have collected contains details of weaponry the Guardians developed.
The guardians’ projectile weapons utilised electro-magnetic propulsion, much like their space technology. Such weapons were manufactured in a range of scaled, from personal weapons to capital-ship class. Generally the Guardians used
kinetic energy in combat, and explosives were rarely deployed. Nuclear fission and fusion were developed during the Guardians’ astro-expansion period, but
when it came to large-scale destructive weaponry they relied on bespoke biological weapons. Predictably, these were of little use against the AIs."
In short, I think the Thargoid are organic "Von Neuman" weapons left behind after the Guardians died out.
The main counter argument I've heard is that the Thargoids biology is so different from the Guardians. Thargoids' native environment is reported to be methane or ammonia worlds, much colder than our worlds. However, we know they can function perfectly fine in Earthlike Conditions (they've attacked humans in hand to hand combat/small weapons fire in one of the official books, without wearing any protective environment suits).
Ask yourself: if you had the Guardian's ability to create an entire race of soldiers and organic ships to fight for you, would you want them to you use your precious earth-like enviroment/biomass for their development? Or would you rather design them to replicate on worlds with hostile environments to you and still be able to fight in your environment?
Besides, if the Thargoids were an independent race that just happened to fight with the Guardians, why is there no mention of them in the Monolith network? An outside, hostile force, surely would've caused the Guardians to pause their civil war to deal with that threat. At the very least, they're would be some note of them in the network. And finally, why would the Thargoids be vulnerable/hate something like a Guardian Relic if there was no relation? No, I propose they're destroying any Guardian tech they run across because it reminds them of their former masters AND/OR they're may be a some kind of "Kill Switch" in that tech that is a direct threat to the Thargoids.
I'm sure we'll find out in time. But right now, the evidence keeps mounting for my (and others) hypothesis that the Guardians made the Thargoids. The latest CG, where Liz Ryder wanted the Guardian Relics to design her AX weapons is just the latest piece. She didn't want Thargoid bio-samples of any type. No, she wanted Guardian tech.
So, why doesn't Guardian tech kill us? Either we lucked out on a cosmic scale (being from a similar planet with similar conditions and developing into a similar creature) or we are related.
As for why Guardian tech doesn't kill us - why they may have had some had in tinkering with our evolution, I don't think we were they're bioweapons. However, they may have still put "Kill switches" in us as well. Please see the article on the lost Generation Ship whose logs indicated that the crew received an a signal of unknown origin from a planet they passed. Anyone hearing this signal goes crazy and tries to kill everyone around them. Even when they know the signal causes these effects, if you hear it, you lose control and become a mass murderer... as the person who dictated the logs became." Then there is the Generation Ship where the female gene completely disappeared from the gametes of all the crew, causing them to slowly die off as they could no longer create female offspring. And then Generation Ship that ran across a pathogen that wiped out the whole crew... a pathogen that had been in space for untold years, and yet was 100% fatal to humans." Oh, I think the Guardians left a lot behind to deal with us - and any other creations - that got out of hand. In fact, the Rogue AI faction/Exiles may have survived and been behind those tests. However, that's just speculation at this point.
But again, the Guardian artifacts themselves don't harm us because we weren't their bio-weapons.