Using Monopoly and Socialism in the same sentence is an oxymoron.
There where some socialists who thought monopoly was a stage on the way to socialism emerging almost spontaneously out of capitalism as a consequence of just economic development. Marx thought that monopoly was "socializing" private property quicker than any socialist party, mind you they'd not so much as formed parties and won election by the time he was writing really.
In the US Edward Bellamy, who was a nationalist rather than a socialist strictly speaking but he wrote utopian novels and was egalitarian (his second great novel was called Equality), he thought that there would be an "age of Trusts", ie monopolies, which would give way to the "Trust of Trusts", ie a single monopoly owning the others, which would then require democratic control if it wasnt to be simply a tyranny like the kings of old.
The best socialists knew that this idea of monopoly being a good idea or even just a neutral stage of development in the economy was bogus.
Rudolf Rocker was a syndicalist and an anarchist but he refers to himself repeatedly as socialist too in his book Nationalism and Culture he repeatedly says that freedom and socialism must be the enemy of every sort of monopoly.
I also dont know all the facts of it but so far as I know the guy who invented Monopoly the board game did it originally as a sort of teaching tool to explain how awful they thought capitalism was and how eventually it would become impossible to play the game, they even suggested to drive the point home that people should try joining the game halfway through play when the other players had already built up property portfolios and bought houses and hotels and see how far they got.
There's a lot of people who're radical proponents of capitalism, who love the fantasy version of it (which sure is fun), they've never liked the potential for the game to show the system in a less than favourable light. So stuff like this doesnt surprise. Conversely there is a game, Class Struggles or Class War or something like that, where people play as bosses or workers, which is similar, but was produced by marxists who thought that Monopoly was not anti-capitalist enough.
Its strange that anyone who is for capitalism would attack public monopolies too much as most of the same arguments would apply to private monopoly which IS the dominant shape of capitalism as it exists and pretty much as any economy shapes up to be.
