The fact that we actually were enforcing antitrust at the time absolutely prevented MS from getting a strangehold on the consumer internet as it was taking off. It's the reason you're posting on this forum in the first place, as it was essential to the success of tech startups in the first dot-com era.
Then we stopped enforcing antitrust laws, and after about 10 years or so the new market leaders had developed the stifling set of monopolies we're all dealing with today.
Breaking up Google (which seems inevitable, this is the third distinct recent case where they've been proven to be a monopoly) is likely to be good for literally everyone, including even Google shareholders.
Unless the argument is that shareholders don't know what's good for them.
https://en.wikipedia.org/wiki/Principal%E2%80%93agent_proble...
So when we talk about "the shareholders" we also include the CEO.
I guess the argument here is that that actually doesn't work and the CEO would prefer being in charge of a larger company even if it personally costs him tens or hundreds of millions of dollars.
That's what I'm skeptical of.
And just in general the incentive of management is to preserve monopoly because it’s a lot less work to sit and collect monopoly profits than to actually compete and win.
The principal agent issue here is that management can sit on their ass all day and make a lot of money instead of working like hell to compete and possibly getting replaced but ultimately creating more shareholder value.