Then what do you call it when people are imprisoned for criticizing Islam.
Whilst I agree with you about the dangers of impeding free speech, the gentleman, Darren Conway, is not quite the innocent you paint him out to be.
Firstly, he is BNP and has links to even more extreme British far-right groups. (I assume you know about the BNP if you dont know what the BNP stand for, you shouldnt be posting in a UK thread)
Secondly, you dont get 12 months in the UK for putting up posters. And certainly not as a first offender. You get 12 months if you have previous convictions. And Mr Conway has himself posted on RationalSkepticism.org that he had a previous charge of assault against him.
Thirdly, he deliberately plastered his windows with posters defaming Islam in pretty crude terms. Posters designed to be seen. He must have thought he couldnt be arrested as they were in his home. Clearly he isnt the brightest person.
Fourth, a quick check of the news on the old interaweb finds that Conway sacked his lawyer and represented himself. Again, not a smart move.
Conway was also found guilty of drug dealing.