Admittedly, I haven't been paying a lot of attention to what Hickman's doing in his Avengers books, but as I understand it, these Earths from other universe keep trying to roll in the the 616 and if they aren't stopped, the universe (or maybe the multiverse) will be destroyed. Which is how you get the Illuminati guys blowing up said other Earths, and Captain America getting bent out of shape over the, you know, widespread mass murder of sentient beings.
Stark, Richards, and the rest would presumably argue they looked into every other option and couldn't find one that didn't involve destroying the other worlds, so this was the only way to save existence. Which seems a little dodgy given some of the challenges they've overcome in the past, but that's on Hickman, not the characters. They're only as smart as he's willing (or able) to write them.
Here's my question: Where are the cosmic big shots? If one of these other Earths completes this "incursion", the universe goes poof. Where's Galactus? The Celestials have spent millions of years or more messing around with the genetics of various species. All the work goes for naught if the universe ceases to exist, and presumably, so would they. Yeah, they can move through time and space basically at will, but they still need some time and space to move through, you dig? The Stranger doesn't care? Eternity doesn't care? Isn't he the universe, wouldn't he therefore die when the universe did?
Are they somehow oblivious to all this? I can understand none of them caring if the Skrulls decide to conquer Earth. That's largely irrelevant to beings on the scale we're discussing. But this would affect them too, so you'd think they'd take an interest. And it isn't as though they'd object to destroying inhabited worlds. During Infinity Gauntlet, the Celestials threw inhabited worlds at Thanos strictly as an (ineffective) diversionary tactic. Like they're going to blink at wiping out a planet to save their skins. Hell, just sit Galactus in front of whatever tear in space the planets are coming through with a lobster bib, and tell him to go to town. At least someone will be getting something out of killing billions of people.