Well, McDonald's isn't trying to sell burgers (directly) here so much as a corporate identity. We are ultimately hurtling down a path of respect and acceptance (which is what evokes such vitriol from the social conservatives at this point--an attempt to stop the unstoppable) and this is a smart move by McD to place themselves on the right side of history.
And by right, I mean cool. Think of the corporate identities of Apple and Microsoft, as an example. Ask for public opinion, and no doubt one company (Apple) will be perceived as cool, while the other is conceived as slow and always in catch-up mode. Even if you never eat at McDonald's, an ad like this gives them a shot of perceived coolness and better, more positive, brand recognition.
As for a version of this ad possibly running in the US, I'm sure McDonald's would target it to mostly urban markets to make better use of their advertising dollar as well as to avoid controversy. But they have to come into this, whether it is in France or in the US, knowing that there will be some controversy... and--in yet another stroke of marketing genius--any buzz is better than no buzz at all.