Yeah, I know you're speaking of customs. But customs never should be used as an excuse for illegal behavior. Its like saying, yeah there was a lot of child abuse in the seventies, but it was the custom back then (I'm not comparing child abuse complacency and over-reaction to photography, I'm making a point about the structure of your argument).
And, plus, your lecture of the French customs is radically different from mine. I do not recognize myself and my compatriots in what your describing. Never saw someone react like your saying of photography. So maybe... you should remember that you're not Levi-Strauss, you just saying what you think about french... It's a commonplace your spreading like "French people are cocky and smell" or "Americans are stupid, you know that they don't believe in evolution". What you're describing is at most a fringe behavior. Neither you nor I are sufficiently aware of the inner complexity of French society (or American, of Papuan) to make so bold judgments. You say it's normal. I say it's not. Who's right ? I'm as French as you are, and no less expert than you (by no less I mean => Not at all). It's you say, I say. No solution for it.
Then you say that it's not about the letter of the law, but how it's enforced. Ahh, then we are coming to a matter that I know a little better than anthropology, see, because I actually had to deal with the police, I've spent time in prison (happily not as an inmate), I've studied law and you know... it's applications. Because, even if a lot of people think we keep our heads in the letter of the law, we actually spend a lot of time trying to understand what's actually the practice of it. And heck, I even had to go report some small felonies that against my very person, and not other people.* And what you're reporting as the "attitude" of the police, is pretty much what almost every layman think of them. Because most of the population despise the police, and think they're useless etc. etc. But you know what, It's not accurate. Yes there is some truth to it. Yes the police won't do all that the law ask them to do. Yes they do a lot of abuses (holy shit, a "PV d'arrestation" is some of the funnier readings you can find around, it's what I read when I need to take a break). And yes, you can come up with a lot of stories of people who had terrible experiences with them (but yeah you know what, no one who had good experiences with the police brags about it), and cases where the police did nothing about a serious case etc. etc. The French police tv series like PJ, Navarro, etc. are full of those. But, well, go to a tribunal, and look at the roll of cases you'll see that the second or third chief of accusation is "violences volontaires ayant entrainé une ITT de moins de 8 jours" (behind small drug related affairs and small theft). But you're right almost half the time it's not because of the 222-13 of the Penal Code. But under Art. R.625-1 of the same Code (section reglémentaire). It's a misdemeanor, fifth class. 3000€ of fine. It's not much... but you should not forget that the 21 special cases described in the 222-13 that transform the misdemeanor in a felony are really broad. And in the situation described, it is almost certain that the Special case n°8 is qualified (if more than one person participated in the assault, but there is a lot of special case so broad as : if the person was drunk or under effect of some drug, if the person acted upon premeditation, because of the race or sexuality, if the victim is an infirm, pregnant, old, under 15 etc). The Public Ministry knows how to make sure you can be arrested under the 222-13.
But, then anyway, even if you fall outside of the the 21 special cases, you can still have a financial penalty.
And by the way, even if ITT has the word Travail in it (work) it has nothing to do with your work capacity (yeah I know, it's an horrible name, legal people are trying to change it to Total Temporary Incapacity)(heck, how would we measure it for babies?). It measures how your day-to-day life was affected. If your disturbed in your normal routine (be it crying all the day for mommy to clean your mess if your a baby) for a week, then you have an ITT of 7 days. But if your emotionally distressed for a week... it's the same. Even if you can still go to work. Anyway, as I said, is a standard measure used by doctors to communicate with the Justice. Break a jaw, and you've got 15 days. A nose ? Between 6 and 20 days. Bruises ? 3 days. Difficulties to sleep after the fight because of stress and nightmare ? between 2 and 10 days (depending on you capacity to lie to the doctor). Got two of those ? Sum it.
So yeah in a bar fight where you only end up with some bruises, no one is going to the jail. Only a 1000€ fine, and 500€ in damages most of the time. But a fight of 2 picking up on somebody ? Felony. And it's what we have there.
But why are you talking about this ? I thought you were all about how the laws are enforced and not the letter. Well, and you know what, based on what I've seen (Créteil/Bobigny) (and it's maybe anecdotal), those kind of cases clutter up the Tribunal de Police. Seriously. And to a lesser extent, the Tribunal correctionnel. And in a lot of those cases of "small" assaults, there was some kind of non-violent provocation. Of course if you punch someone in the face and get punched back, the case is not going to a tribunal, but if you say : Fuck you to some one and get a big punch in the face, you should go to the tribunal, your probably winning easily, not much, but still, somewhere a policeman will hear you and send your case to the Public Ministry, who will be pissed off, with this, but at least make a Rappel a la Loi if it's a misdemeanor.
So in this case, where there wasn't even a provocation in my understanding (but for you, it seems that all French people get mad at people taking photos), there is no reason not to follow up and pursue those 3 guys at MacDonalds. And from my experience, had he been French or at least European, the police would have (maybe they are and we do not know) (Well... if the story is true... obviously).
I've actually met a person in jail who had punched someone in the face, after being called son of a bitch, but the victim fell with his head against a chair and passed out for several hours. The perpetrator was in recidivism situation so he ended up with 6 month in prison.
In plain English : Please stop saying what things ARE. And start saying what you feel/think things ARE. Principally when you're speaking as if you where an expert, and mainly conveying "conventional wisdom" which most of the time is not totally accurate, to be kind.
PS : You should read the annotated version of the law, you know the 'Code Penal' Red Book by Dalloz, not just legifrance. Because legifrance does not have the jurisprudence, and analysis of articles and interconnections in the law.