afleitch: Yes, I think the subjective nature of what constitutes ‘mockery’ is indeed the problem with, or at least the difficulty of, holding this position—I think at a minimum I’d say that to constitute mockery something has to be in some way targeted towards addressing whatever the issue is on whose basis it’s claimed to be mocking. The ham sandwich and gay marriage examples are clearly not intended to comment in any way on what they’re purportedly mocking.
I'm aware that this isn't necessarily a sufficient distinction to make and that the question remains subjective and liable to case-by-case judgment calls, in any event. Which, again—the difficulty of holding this position.
I think my problem is that you're suggesting (and the Pope obviously) we have this 'distinction' in terms of religious belief systems which I profoundly disagree with (because they are no more than systems of thought/morality/philosophy) That aside, even if I did agree with the need to be 'careful' I can't honestly trust nor expect religious bodies or religious people to properly determine what is 'mockery'. There is no rational/reasonable basis for them to do so, because religious belief does not operate according to those lines. I find it as impossible to 'offend god' as it is to offend pixies (and I make no apologies for a 'cheap' comparison.). It's just not possible for a non-believer to offend some being that cannot express how offended it actually is. People are a different matter of course, but nor can they express their offence on behalf of god for the same reason. And that is essentially what blasphemy is.
I don't see why the question of if God exists or not is relevant to blasphemy, blasphemy is and always has been about the sensibilities of believers, not their deities. If there were a widespread fairy-believing movement, you could blaspheme against them as well, no need for fairies to exist.
In any practical sense, at least, God is as real as "freedom of speech" or any other nebulous non-physical concept...it exists at least as much as you believe in it.