Some of the bods you mention were professional political agents-provocateurs in the publishing trade, which many of the recidivists were. A few once-only offenders may have been accidentally caught up in what was, at the time, a very 'vigorous' and fairly free-for-all political press, including the widespread publication of anonymous pamphlets. I think the prosecutions have to be seen against this background.
I'd be interested to see some examples of the sort of stuff that was objected to and the sort of stuff that wasn't. Compared to today...? One thing that impressed me was Wellington complaining about officers writing home their descriptions of how he botched some campaign (while on campaign!), and its being printed in the papers - and his inability to prevent this. That sounded like a relatively free press to me - and certainly much freer than today.
Montgomery-Hyde in his History of Pornography, has some useful discussion of pornography prosecutions.
Cheers
C