Well, if you really want a concise answer, I choose to avoid online coop play chiefly because it brings out the worst of people, who have no motivation to play fair, but due to the anonymity of the setup, have every encouragement to cheat, disrupt, and ruin the fun of the thing for as many as they can.
You can see them in most all the online forums devoted to MLB The Show. They are the ones that recycle the same complaints, centered on demands that SDS focus on their desires and whims to the exclusion of all else -- as if they alone are the center of the effort, the sole benefactor of the effort.
But worse, you see them in threads devoted to showing how they employ cheap tricks to trade sportsmanship for empty wins. It only takes a brief review of the threads to see this.
I want nothing to do with such people.