Atmosphere as a general rule of thumb in this country tends to be reactive, not proactive. Attempts to improve matchday atmosphere such as the use of drums, clappers and the formation of ultras groups (like Palace have) are often greeted with derision and accusations of being tinpot. Widespread, organic, non-stop generation of atmosphere just doesn't tend to happen anymore for a variety of reasons; many have already been stated.
Sorry to butt in - but it is that time of the season again.
I like to think that The Den still retains some of that old fashioned organic support you speak of. Okay, it isn't like the days of Cold Blow Lane, but for modern football is still pretty partisan and in an organic way.
The reason I think this is, is because Millwall have never, ever, had any kind of sustained success. So, what you are left with is a fanbase made up of 'hardcore' fans.
And they would have to be pretty hardcore, as not only have we never had any sustained success, but we are also surrounded by much bigger and more attractive clubs to support - our catchment area is literally the neighbourhoods of Bermondsey, Deptford, Rotherhithe, New Cross, Peckham and Walworth. Plus we have the worst fan reputation in English football. I mean, you must really want to support Millwall to, erm, support Millwall. I would argue that 95% of the people in the home stands can all trace their roots back to docklands London, either in the neighbourhoods mentioned or from the old EastEnd communities just over the river & where the club was born.
What I am saying is that we have never been diluted as a fanbase. I think more and more clubs in the top half of the football pyramid have. Their fanbases are now made up of not only hardcore fans, but by more affluent supporters, especially families attracted by football's modern image. In SE London those people go to Palace or Charlton; or Chelsea/Arsenal/West Ham if they can afford it / get tickets.
And you are less likely to burst into song or swear at the ref / opposition if you are sat next to a nice family eating their popcorn (hello West Ham!).
At The Den our stewards have a pretty lax attitude to swearing or sitting. In fact, the club has a policy of sit where you like in a block - no looking for 'YOUR' seat. There is no your seat. This means mates and family get to sit together more easily, which I think helps with this creating an 'organic' atmosphere you speak of.
No doubt you will look left and right from the away stand on Saturday and sneer at the pantomime put on for you. Mostly young men playing at parodying the old Millwall dockers. Yes, it is a bit silly. But, look a bit closer, they are all standing, it looks a bit like an old fashioned terrace scene, they are swearing and singing together and look like they are having a laugh. And if it turns into a bit of a firey game the whole ground will begin to look like that. And if you tut or sneer at them, well then ask yourself how do you create a good atmosphere if it needs to be a bit sensible, a bit controlled.