I try to picture Milton, sick, going blind, bitterly disappointed at how their political hopes just fizzled out when Cromwell dies. Then another bitter stroke, CharlesII comes back with the most unrepentant hedonistic court possible just to put the boot in, plus claims his father was now canonised!

I think that by glorifying the highly unlikely character of Satan, in a way that is not in the bible I think Milton is making a very strong ironic protest statement about injustice on a human level.