Man if you weren't so off-base dumb-concerned over monopolies (this deal BTW doesn't create a monopoly, read up on what a monopoly actually is) you'd recognize the forest from the trees: MS's intentions aren't to "destroy" Sony or Nintendo like fanboys think. Why would they? If Sony or Nintendo are destroyed, that creates a vacuum for Apple, Google, Amazon, Tencent etc. to come in and fill the void.
That doesn't mean they won't be competitive with their newly acquired assets; it just means they aren't out to choke Sony or Nintendo to death. There'll always be some form of Activision-Blizzard (and Zenimax) software support on Sony and Nintendo platforms, especially if those platform holders work out a deal for GamePass on their systems (probably tailored to their ecosystem in some way).
Put it another way: if Microsoft didn't buy Activision-Blizzard, Facebook would've. Or Google. Or Tencent (btw Tencent have shares in Activision-Blizzard they'll still retain post-acquisition). And while all of these major tech/entertainment conglomerates (yes, including Sony) are at least partially involved in things benefiting various governmental bodies that may not be at the peak best interest of us regular folks, out of the companies looking to buy Activision-Blizzard, Microsoft are the least offending of those options by a decent mile.
Also I don't see how you blame the buyer when the seller approached the buyer with the proposition to begin with