It is very well known the Covenant’s most preferred way to dispatch of a human colony is by ‘glassing’, but what isn’t is that humans did much the same to other planets.
The Covenant justify their procedure by getting rid of human filth.
The Ancient Humans justify their procedure by getting rid of flood filth. They also may have (Not entirely certain!) glassed (cleansed as they called it) some of the planets or colonies belonging to some of the species of the Covenant we know today.
If you take a step back and think about it, it is very ironic that we glass planets, and 100,000 years later it comes to bite us back.
I was thinking this exact thing the first time I saw that terminal. XD
“Huh… the Covenant really DON’T have any original ideas, do they?”
Well, we dont really know for certain whether the Forerunner would have placed the same species on two different planets, but I highly doubt it. From what we see in the terminals, the species of the Covenant were rather primitive during the time of the Forerunners (except the San’Shyuum of course), so the fact that these species were indexed for reseeding kind of indicates (to me) that their planets werent glassed by ancient Humanity.
I think the fact we were best buds with the Prophets is a lot more ironic than the fact both used glassing.
I’m pretty sure the Halo 3 terminals mentioned the forerunners employing glassing too.
Interesting to note though, in Thursday War, Jul does compare humans to the flood 
In no way is it even remotely the same.
The Covenant glass planets on theological and ideological basis. They avoid completely destroying the planets, and avoid Forerunner artifacts.
Ancient Humanity “cleansed” planets due to the Flood, an actual threat to the galaxy. When it shows them preparing to glass the planet, one human asks if they should warn them, to which Forthencho says that by the time they did it would be too late. Keep in mind that the Flood was far more advanced and dangerous than the Flood we encounter, having considerably more time to advance to such a state.
> If you take a step back and think about it, it is very ironic that we glass planets, and 100,000 years later it comes to bite us back.
Better it biting you than the Flood. There’s not that much ironic about it really. The Covenant did what they did needlessly at the end of day.
Not very ironic. As its mentioned, one was needed and the other one was just war.
> It is very well known the Covenant’s most preferred way to dispatch of a human colony is by ‘glassing’, but what isn’t is that humans did much the same to other planets.
>
> The Covenant justify their procedure by getting rid of human filth.
>
> The Ancient Humans justify their procedure by getting rid of flood filth. They also may have (Not entirely certain!) glassed (cleansed as they called it) some of the planets or colonies belonging to some of the species of the Covenant we know today.
>
> If you take a step back and think about it, it is very ironic that we glass planets, and 100,000 years later it comes to bite us back.
The races within the Covenant do not posses the ability to create, instead they imitate. It could be the lack of Forerunner artifacts on Earth when humanity was redeveloping after indexation, causing them to evolve creative abilities in order to survive. The Librarian probably removed most artifacts from the humans grasp to give them an evolutionary advantage. Having the remains of a Tier 1 civilization on a planet would certainly sever natural selection for a species, making it unnecessary to develop their own technology when they have it all waiting for them. This gave the humans the advantage of innovation, but to the point to where it blocked the other species ability to evolve, the Librarian has clearly committed crimes against the Mantle for oppressing bio-diversity on a Galactic level.
As this knowledge of the Human-Forerunner war was stored within Forerunner artifacts, it’s not a surprise that “glassing” became a sort of archetype for these races.