Work/Life separation. Really?

I noticed that many people emphasize and take pride in their ability to separate their work and non-work time (some call it having a “personal life”). I realize that this is a charged issue. I can understand it but not agree with it. There are so many seminars, workshops, and books that teach us how to separate between life/work and such. 

I agree there are many advantages to such a separation, especially in times of stress and pressure at work, however, this time I wanted to challenge this idea and question it: 
Is it really necessary to separate the two? Is it even possible?

Here are three thoughts that may paint the separation between work and “personal life” in grayish colors:

1. EVERYTHING is personal.
   For years, I believed (and still do partially) that things that happen to us in life are a direct result of who we are. There are philosophers and psychology researchers who developed theories that explain that there is no reality but the reality as WE perceived it- the subjective reality (e.g. Thomas Nagel) . If we follow that line of logic, we cannot really separate between our personal and professional aspects since both are a result of how we perceive the world.
   
   
2. Humans are complete systems.
   (I am using the word systems as an attempt to avoid the word “holistic” that I would have really wanted to use here, since I realize the risk of losing some of you by sounding too fluffy...)
   
   We present different identities in different situations, we reveille certain aspects of our personality with friends and family (e.g. we might chose to act goofy and foolishly since we know we are in a safe environment), with colleagues at work (we might chose to act in a very focused and serious manner), etc.
   
   Even if we chose to behave completely different in certain scenarios,  we are still the same person and therefore it does not seem possible, sustainable, or effective to turn certain “parts” of ourselves ON and OFF
   (or do you think we are all suffering from a split personality syndrome?)
   
   
3. Passion.
   - People who are passionate about what they do, want to do it all the time and can’t help but think, talk, and act about the things that they are passionate about.
   - Lucky people are passionate about their job.
   Should I draw the conclusion that people who insist of separating their lives are just not passionate about what they do? 

Maybe instead of trying to separate the two we can focus on 
how to balance them.