While passing one of two Quick fast-food restaurants (the main competitor to McDonalds) on the Champs, I was surprised to see that it was closed, with a notice on the windows that said it had been closed by police headquarters for nine days because of “noise and disorder.” I'm not exactly sure what that means, but I suspect the restaurant was being haunted by various scum from the suburbs, now that the Champs is increasingly becoming a meeting place for gangbangers and other losers in the wee hours. I also suspect it's not the restaurant's fault but purely linked to the fact that Quick is one of the few places that stays open after midnight on the avenue.
The area around the Champs is deteriorating because of the dregs that ride in from the suburbs on the express subway (RER) at night and especially on weekends. After laying waste to their own neighborhoods, they apparently want to make a shambles of one of the world's prettiest cities as well. They like to fight, and I guess they need a pretty stage on which to do it. I've already mentioned in other posts some of the changes that have taken place. On parallel streets I see more and more clubs of questionable reputation, too. They look suspiciously like the bars you used to see in Pigalle. I'm surprised that the city is not doing more to prevent this kind of deterioration, as the Champs is very popular with tourists.
There are a couple of hot spots that police have identified as being popular with gangs (some of which are now based in Paris, alas!), and the Champs-Élysées is one of them. The Gare du Nord train station is another, although that part of town has been rather seedy at night for years (unfortunately, it is also the train station that serves the Eurostar). The Forum des Halles is yet another spot that gets a bit weird late at night. I still wouldn't call any of these areas dangerous, but they seem to be gradually getting worse. I hope something is done about it. I prefer that the losers stay outside the city.