this article by Nathalie Bonney on the Good Housekeeping website.
The broad argument is that to show solidarity with the French this way is parochial. There have been thousands of people killed by terrorists this year, and yet no one is putting up flags of other locations. (Actually, not no one - one of my Facebook friends has made his own Lebanese flag cover for his Facebook photo.)
I have two problems with this complaint. One is that it seems petty to discourage someone from doing something positive for one group because they aren't doing something positive for another. It's a bit like saying 'I would never give any money to Cancer Research because I'm not giving anything to the British Heart Foundation.'
The response from supporters of the objection, I guess, would be that the argument is more nuanced than that. They don't have an issue with showing solidarity with France, but it's not fair that it took an atrocity in France to generate this kind of response from Facebook, and there wasn't an option for previous atrocities.
I would suggest this reflects the false 'small world' impression given by the modern media and many commentators. Because we can see disasters happening anywhere, we think that it is possible to have exactly the same attitude to an event wherever it happens - but that is totally unnatural and if we are honest and not self-deceiving, it is impossible to truly do. The fact is, I will always feel closer to, and more affected by, a disaster in my family than one to someone else who lives down the same street. And I will be more affected by a disaster to someone else in my street than to someone who lives in London. And I will be more effected by a disaster in Paris, a place that I have regularly visited and that has strong cultural ties with the UK than I would by a disaster in the Middle East.
We can't feel the same about everyone and everywhere. This doesn't mean we ignore things outside our own neighbourhood, but it is entirely natural, and should not be a matter for criticism, that we put more weight on events that are closer to home, physically or culturally. To try to feel exactly the same about everybody and everywhere is both inhuman and impractical, leading to a cold, thin porridge of a response. or universal outrage with no focus.
So, while, as it happens, I have not added the French flag myself, I think entirely fine that other people have, and consider the criticisms misjudged and unnecessary.