Asymmetric laws and asymmetric justice
> As an example of this, it is an offence in France to insult a public official
Having something illegal in one part of the world and legal in another is just one, small, part of the issue. The other is enforcement.
Without enforcement, laws mean nothing - as anyone who's accidentally stuck an upside-down stamp on a letter¹ will be relieved to know. Likewise, if a resident of one sovereign nation commits an offence in another country, if makes little difference unless the "victim" country presses for extradition and the "home" country grants it. Sadly for us, the UK seems to regard shipping individuals off to be tried in other places, sometimes on the flimsiest of pretexts and with scant evidence of a case to answer, to be a means of saving money by outsourcing law enforcement, rather than a duty of protecting it's own citizens' rights.
So, apart from the question of "is it legal", there should be a bigger question of "will anyone care enough to do anything about it?"
Further, we are all told that ignorance of the law is no defence. However, it would appear that we are now all personally responsible for knowing all the laws in every country (and in every language, too) else we could find that an innocent typo means something completely blasphemous (to take an example) in some place we've never heard of - and we're about to become the new "friend" of an inmate in a jail on a distant continent.
It does seem to me that this state of affairs is neither practical nor just. Law-abiding people who innocently transgress some foreign diktat via their internet activity should not become criminals, simply because some faraway place objects something they have published. Conversely, there are some behaviours that are quite legal elsewhere, that we - or others - would find objectionable.
What is the answer? Well, short of every country burying their differences and coming up with a common legal framework, judiciary and scale of punishments, I can see none. With the possible exception of making the whole enforcement issue moot by ensuring that your internet activity cannot be traced back to you - though that in itself is probably illegal somewhere.
 The 10 stupidest laws - though #6 might even be worth getting pregnant for.