I'm late to the discussion and haven't read the entire thread. Forgive me if I am raising a point already made.

"If you could press a button that would turn everyone into brains in vats living the best possible lives imaginable would you do it?"

Would each person be isolated or would they inhabit, via an avatar of some sort, every other person's virtual world? In other words, will they be networked? Will the other people be real or "non-player characters" driven by an AI and lacking subjectivity? If each person would be isolated in a virtual world of their own, then to press the button would be to condemn them to a largely meaningless existence devoid of the possibility of true encounter and morally significant action. And such a life cannot possibly be the "best possible life imaginable".

I'll put aside my small quibble that any virtual world must be far less rich than its host world, which would nullify any possibility of it offering the best life imaginable. If everyone would inhabit a common world and interact directly and share experience and affect one another, then I don't see much problem pressing the button. I don't see how it would be existentially much different than the world we inhabit now. The other people in the world would be real. There would be someone else, an end-in-himself/herself, on the other side of each encounter, someone who must experience what is done to them. The world would have depths. Of course, this challenges the notion of "best possible life imaginable" that most probably have in mind because it would be possible for people to treat each other in unloving ways and to obstruct their will.

Also, I suspect that most people, in dreaming of some scenario that would constitute "the best possible life imaginable", are envisioning a life without suffering, death, struggle, poverty, limitation, and so on. It seems to me implicit in the question that such a life would be one in which each person has limitless power, resources, access to aesthetic experiences, fine surroundings and possessions, and so on. In my view, such a life would be pure fluff, like living in a kitsch painting, empty of real and substantial life, completely hollow and superficial. It would be strictly masturbatory. Despite all appearances, a deep desolation would permeate everything. By far the greatest impoverishment in such a life would be the absence of other subjects with whom one might enter into the Ich-Du. This "life" would be always strictly in the mode of Ich-Es.

It would seem that to make life in a virtual world substantial and deep, you'd have to bring into it the very sorts of conditions that we find ourselves confronted with in this world that we would presumably be trying to escape by creating such a virtual world. So what would be the point in leaving the real world?

Hi Oysteroid, welcome! Hints of Liebniz, there.

Would each person be isolated or would they inhabit, via an avatar of some sort, every other person's virtual world? In other words, will they be networked? — oysteroid

Like two people on other sides of the world each with a chess board before them, versing each other.

In my view, such a life would be pure fluff, like living in a kitsch painting, empty of real and substantial life, completely hollow and superficial. It would be strictly masturbatory. Despite all appearances, a deep desolation would permeate everything. — oysteroid

But even if this was so, you wouldn't know it. Because this is the best possible world, you'd experience the world full of 'real and substantial life', moral significance, and meaning. You may in fact be alone, but you would have no knowledge of this and you'd act and live as if you were among others. Is this really much different to the way in which we exist now?

So what would be the point in leaving the real world? — oysteroid

Suffering. This world is full of it.

'The only way out of it is through it' ~ anonymous saying

actually it's not an anonymous saying, it's from a Robert Frost poem:

'The best way out is always through'.

If one were a utilitarian who believes that:

(a) brains in a vat were the sorts of creatures due moral consideration,

(b) brains in a vat could be virtually identical in terms of all relevant (at least moral) qualities to brains that are further embodied and interactive with the world via those bodies' mobility,

(c) pleasure and/or happiness per personal assessments is what should be maximized for the ideal good to obtain, and

(d) brains in a vat could be such that (b) obtains and those brains have maximum pleasure and/or happiness assessments,

then one would have to say that they'd press the button.

That might work, but is it really saying much?

How things would be set up in this kind of scenario, I would answer pretty much as dukkha has.

For example, there might have to be alternative realities operating. More than one person might want to win the Nobel prize for Literature, for example.

Of course the other in this virtual world will not be real; this is the point of the thought experiment; does reality matter or does quality of experience trump it? Would it matter if none of the other characters in your virtual world had their own inner experience if there were no way you could tell?

Think of the Matrix movies, for example. Are the characters in the Matrix really interacting with one another; or is each person living inside their own simulation?

Also, I suspect that most people, in dreaming of some scenario that would constitute "the best possible life imaginable", are envisioning a life without suffering, death, struggle, poverty, limitation, and so on. It seems to me implicit in the question that such a life would be one in which each person has limitless power, resources, access to aesthetic experiences, fine surroundings and possessions, and so on. In my view, such a life would be pure fluff, like living in a kitsch painting, empty of real and substantial life, completely hollow and superficial. It would be strictly masturbatory. Despite all appearances, a deep desolation would permeate everything. By far the greatest impoverishment in such a life would be the absence of other subjects with whom one might enter into the Ich-Du. This "life" would be always strictly in the mode of Ich-Es.

This is not necessarily the case. For example the experience of Charles Manson would be quite different to the experience of Jesus. So provided the person was of the right mind, it would be ok.