The "Areopagitica" was Milton's response to government's plans to enact censorship laws on writers. He did not want the government to be given control of publishing because he felt, and rightly so, that this could lead to the suppression of thoughts and ideas. He preferred that accountability for writing should be controlled by other means, at the editorial level within the publishing cycle, for instance, instead of at the governmental level.
Milton felt that freedom of expression was an integral aspect of education and learning, of the development of humankind. He writes:
Where there is much desire to learn, there of necessity will be much arguing, much writing, many opinions; for opinion in good men is but knowledge in the making.
He also believed that taking control of thought away from thinkers, researchers, teachers and the like would render that thought useless to the world, stating:
And how can a man teach with authority, which is the life of teaching, how can he be a doctor in his book as he ought to be, or else had better be silent, whenas all he teaches, all he delivers, is but under the tuition, under the correction of his patriarchal licenser, to blot or alter what precisely accords not with the hidebound humour which he calls his judgment?
Lastly, he thought that the censoring of writing was just the first step on a slippery slope that would lead to the censoring of all artisitc expression:
If we think to regulate printing, thereby to rectify manners, we must regulate all recreations and pastimes, all that is delightful to man. No music must be heard, no song be set or sung, but what is grave and Doric. There must be licensing of dancers, that no gesture, motion, or deportment be taught our youth, but what by their allowance shall be thought honest
Knowing what we now know of the long legal history of battles against artistic censorship, one cannot help but see that Milton's fears were quite accurate!