"Oh, those Covenant fools! They must've known, there must have been signs!

The Covenant...found something...buried beneath the ring...something horrible...and now, they're afraid."

So at the start of the original trilogy the Covenant unknowingly (and if we were to agree with Cortana, then also somewhat recklessly) released an unmatched evil to an unsuspecting galaxy.

Now, at the start of the forerunner trilogy, couldn't the same lines from Cortana be used to characterize the chief and her own actions? And no, I don’t mean the buried beneath the ring part.

Of course the chief and cortana were essentially tricked into freeing the Didact whereas the Covenant were most likely searching for relics and other stuffs. But it was frustrating spending a couple of levels running around trying to prevent Infinity from being taken in by Requim when in fact we were only puppets going through the steps needed to release the Didact.

Cortana was quick to admonish the Covenant in H:CE, but how did she feel about the way Chief and Cortana subjected mankind to another evil which is only matched/surpassed by the flood? Probably not her proudest moment – granted empathy was not her strong suit, but maybe she would cut the Covies some slack should had gotten another shot at it.

tl;dr: Covies let out flood in H1, we got angry at their stupidity. We let out Didact in H4, oops!