"the question as to whether states should prevent companies from becoming monopolists"
I believe the general agreement about this question is a resounding "No." The anti-monopoly regulations prevent companies from abusing their monopoly power and most of the anti-monopoly law discussion revolves around the extent of this.
Of course monopolies are not intrinsically evil. I can’t really see what that has to do with the question as to whether states should prevent companies from becoming monopolists, though.