But I think the fair world is a world without compassion and with huge separation between rich and poor. I think on ethical grounds we should make the world less fair, more equalized, despite of the fact that it reduces GDP growth, because there are other metrics possible, like human happiness and well being.

I'm a bit confused by your definition of fair, to the point where I think that we hold the same precepts, but we may using different words for them. I would make the case that increasing 'fairness' is equivalent to making things more equalized. I would use both terms interchangeably.

In any deal, if one party has more leverage than the other, in principle it's not a 'fair' deal, even if the disadvantaged party rationalizes that it could've been worse, or that the other party didn't fully exploit the power of their advantage. In the context of labor, reducing the leverage that employers have over workers is evening out the playing field, which I would say is more fair.

To be clear, in an ideal world, neither party would have leverage over the other, and people would work for someone else or with each other only due to it being mutually beneficial in equal measure. In reality, things will never be that 'perfect', but I think it's absolutely possible to remove the more egregious points of leverage.

The people using existing leverages will try to prevent that by removal kicking and screaming because they don't want their advantages to be reduced, however they should try to be content with an equal power dynamic if they consider themselves at all moral. In all other areas of life humans have decried unjust imbalances of power, and I don't see how labor relations would be subject to different rules than, say, competitive sports. We don't stack the deck against one team or the other, we try to make it fair.

So when you say a fair world would is a world without compassion and even more division between rich and poor, I must ask, how are you defining the word fair?