IIRC, Marx actually preached a large government which slowly became "unnecessary" in the long run as people became more socialist. E.g: It'd go from what we saw in Russia in the beginning of the Soviet Empire, to an ultra-libertarian socialist system.
Some thoughts on this.
-Pros
People would say it would stifle innovation and progress in humanity. To be honest, the advances of technology have been made off the backs of slave labour, so yes, it would stifle innovation. Also, the environment hasn't caught up to our progression, e.g: with the melting of permafrost and the knowledge that a hundred years from now we'll all be dead, etc. Slower progression is fine, by my standards, if it means people aren't suffering, or there's less of it.
-Cons
Idealistic. Big governments like staying big. In an idealistic situation, power isn't needed. But that isn't so. Governments retain power, as with the Soviet Empire, to the bitter end.