So we go from tribal-agro-cultures where the tribal group (say 140 people or so) interact with each other on a daily continuous basis. To our current situation where we spend a large proportion of our time interacting indirectly with our social group, passively observing the spectacle (newspapers, television news, gossip columns, fictional tv, documentaries etc.) and for many the direct (unmediated) interaction is limited to the nuclear family and maybe one or two close friends.
In this sense we no-longer 'own' our lives as we have become extensions of the medium (and therefore the media) itself. Just like Marxism warns of the danger of a life mediated by the means of production so SI warns against life being mediated by the spectacle (that is a consensus world view created by a handful of people).
The spectacle though is nothing new, it's been around a long time i.e. history is written by the victors - those that control the media provide the story into which we weave our lives. They describe who the bad guys are, who the good guys are, what is acceptable and what isn't. And it's woven into such an incredibly integrated way that we confuse it with reality.
Of course nothing we experience is fundamentally real, that's basic neurology isn't it ;-) everything we experience is a construct of our senses in-combination with our perception. The vast majority of planet earth is empty void - yet we see everything as solid.
But there are degrees of abstraction - and an authentic life (in the sense of Walden) is one with the least mediation. An example of the most direct experience is anything that allows you to focus on the actual sensory data and it's nature - this of course is the realm of insight meditation. At the other extreme is a life consisting entirely of TV consumption - and most of us somewhere in between.
This all boils down to me as the question are you living your life or just watching it like so much television.
The most radical lifestyle I believe is one in which we choose to actually live, that is to make our own decisions based on an unmediated direct relationship with our own life. Not to follow other people's direction (especially me) but instead to investigate and to try to understand to the best of our abilities how best to lead our life.
It's no co-incidence that both Thoreau and Gandhi referred to the way they lived their life as experiments. Not beholden to some mediated truth but intent on direct living and experiencing reality for themselves.
I think the issue is not about "what lifestyle", thinking is lifestyle terms seems to be a byproduct of living in the spectacle society itself! To me this stuff is first and foremost about truth in life, true freedom, but of course this path is arduous, there are uncountable layers of overly-simplified semi-truths over us.
Interestingly, Debord seemed to have proposed a life style of Derive, aimless wandering, following one's desires. To me, this resembles the mind set that he tries to attack. Both tell individuals "You are a snowflake! Follow your inner desires!"
Maybe the more during counter life style against the fads and suppressions of the spectacle society, is a devotion to objectivity and naked facts.
This was the aim of Thoreau, Gandhi and of course the Buddha - to live life directly without any mediation between oneself and reality. And to greater or lesser degrees they all achieved that.
All these viewpoints, Situationism, Marxism etc. can be dogma or just little clues to help us live a more fulfilling and satisfying life.