There's a difference between what is good for the public, what is good for the market, and even what's good for a business's long term outlook.
The issue with spinning off losers and acquiring winners is the prioritization of short-term gains over long term gains. Further, I dispute that it's motivated by "the market" and not the gambling habits of corporate leaders.
Take, for example, HP's purchase of Palm for 1 billion dollars. But then a few months later, they let go of basically the entire palm staff. Then they created their webos tablet, then they killed it just a few months after launch. Then they let webos linger until finally selling rights to it to LG of all places.
You certainly can argue "this is just the market being efficient" but was it? Or was it overpaid C level individuals making big bets, failing, and punishing their employees for their incompetence?