It would be better if you share why this would hurt all companies if it happens. Let's say that tomorrow Sony jumps in and says that they will also allow all developers to do crossplay if the want. How do you think things will look one or two years after that? I actually think that it is not only beneficial to the gamers to have more options, but it will hurt Sony in the long run if they let the competition unify into basically a single online service. It doesn't look good for Sony when Android, iOS, Steam, Nintendo Online and Xbox Live can all have a single player pool where all gamers can play together and they remain out of that. People seem to forget that Sony has the position they have right now because they gave gamers what they wanted. You could argue that following Microsoft plan of not letting resell the games was the better business decision.
I guess nobody can predict the future, so i guess each actor has to consider very carefully the next step. Maybe allowing crossplay can be a benefit in the short term, but a problem in the long term. Or the other way around.
Also comparing gaming specific platforms vs 'multipurpose purpose' ones like Android, iOS or Windows isn't fair, despite they share some points obviously.
Again, Sony are the ones that have to decide if this is a thing most gamers want, or only a small fraction, or maybe a large number,but most are on competing platforms, so it is a no issue in their real world (at least for now).
I want crossplay, i play KOFIV on ps4 and it is difficult to find games and crossplay with PC won't be available afaik, don't know the reason why, btw, so i am for it, but i also understand that they allowed it somehow with PC and WiiU(if not mistaken ) in the past, but now for some reasons aren't allowing when MS is involved, so i am sure this is under discussion at sony, and also at MS nintendo and other developers and publishers.
My opinion is that this needs an agreement , so we can guarantee a solid future, and not a changing one depending on the managers of the leading platform of a specific moment.