@Pedallleur I grew up in the 90s in a non-smoking household, and to me the smoking in Mad Men was just part of the whole vibe and milieu of it. It wouldn't feel right without it.
But they definitely lean into it, and play on the fact that it was so ubiquitous then, and is so comparatively unacceptable now. In the first series or two, I'm sure the programme makers were deliberately putting in as many instances as possible where a character produces a surprise cigarette from yet another ingenious or ridiculous cigarette dispenser/hiding place — DP and I were watching it trying to guess where the next stash would be secreted.
[Spoilers for a scene from season 2 in the entire rest of my post: don't read anything in italics if you haven't seen that season yet but might want to in the future, as it's better when it's a surprise:]
They do seem to enjoy playing into things where behavioural norms have changed a lot, and occasionally shocking the sensibilities of a modern audience, e.g. the picnic scene in season 2. I think most people watching that scene would have the same kneejerk "What are they doing?!" reaction I did.
It's what looks like a nice, ordinary (if well-off) family, having a picnic in an idyllic-looking beauty spot somewhere. We know them as full, rounded characters we understand as people and can (maybe) sympathise with. We know that they consider themselves upright members of the community, and that they're keen to keep up appearances, present themselves well, and keep their home and garden beautiful. We've seen that the parents care that their children reflect well on them, and that they have high standards for their presentation and behaviour, and aren't afraid to discipline them.
We might notice that they've driven directly to the picnic spot, parked up there, and are playing the car radio with the door open (maybe with the engine running?), and absorb those differences from how an equivalent modern family might behave (or be allowed to behave). Standard stuff for the show, and by this point anyone still watching is used to taking in, and probably enjoying noticing, those differences.
When they're finished, Don suddenly stands up and lobs his beer can into the distance, and while you process that breach of modern cultural norms (maybe wondering if that would've been acceptable even then, or whether it's supposed to say something about Don's character or state of mind), you watch the adults strictly insist on checking the children's hands for cleanliness. The combination feels almost contradictory to a modern mindset — so focused on cleanliness in one way, yet not at all in another. Then just as you're starting to move past the beer can shocker, Betty picks up the blanket, shakes off enough empty packaging and other crap to fill a kitchen bin, and they walk off to the car, leaving behind a pile of rubbish to sit on the grass or disperse in the wind, in this previously beautiful picnic spot.
Nobody mentions anything about it — it's obviously utterly routine, with no hint they think they're doing anything unusual at all. And then straight into the next scene. Clearly played to shock the audience, but not dwelt upon or referenced ever again, like any totally normal behaviour. I don't know how realistic it is as a representation of the attitudes and behaviour of wealthy middle class 1960s people in that part of America, but it's very effective at quickly communicating major differences in mindset. And also, maybe, prompting reflection on things like whether our mindset is really so different, or whether we just do the same kind of thing but in less immediately obvious ways. Or on why it is I'm apparently more shocked by the littering than by the casual sexism, racism and anti-Semitism.
The extent of the smoking, the littering, the drinking, the drunk driving, the misogyny, the racism, and the other differences (or not-so-differences) are part of the point, especially in the early seasons IMO. Things like that picnic scene, cheap trick though it was, were one of the reasons I enjoyed the early seasons of Mad Men so much.