There's no such thing as a large bureaucratic organization that is "good". The larger the scale, the less morality enters into the picture at all.
Making large companies state-owned wouldn't preclude them from being monopolies, it just changes who's in charge of monopoly abuse. With state-owned monopolies you end up with something more like USSR.
No, OP is right: this much concentrated power just shouldn't be allowed, period.
I disagree. The EU one of the largest and most bureaucratic organisations in the world and while they often make dumb laws - especially around technology - it's usually at least with the intent of making things better for people.
State owned monopolies really only make sense for natural monopolies (e.g. transport and communications infrastructure), and I wouldn't really count desktop operating systems as that. Windows is a monopoly due to extremely strong network effects.