If Book 10 is the peak, then one will see the whole book ascending steadily to the teaching that the contemplative life of philosophy is the highest good, because it is the activity of the intellect as the most divine part of human beings. The moral virtues and practical reasoning will be seen as inferior to the intellectual virtue of philosophy as the dominant end or summum bonum for all human beings. Since most human beings cannot live a philosophic life, they are condemned to live a less than fully human life.
This leads one to conclude that the best moral and political order would be ruled by, or at least in the service of, philosophers; and this moral and political order would conform to the cosmic order of the universe as ruled by the divine Mind and the eternal Ideas.
This reading of the Ethics would assume that Aristotle's ethical teaching is ultimately Platonic in its conformity to the moral and intellectual cosmology of Plato or Plato's Socrates, particularly in Plato's Republic and Timaeus. This Platonic Aristotelianism would contradict my argument for the biological character of Aristotle's reasoning and the compatibility of this biological Aristotelianism with Darwinian science.
In contrast to this reading, if one sees the peak of Aristotle's Ethics in his books on friendship, then one will see the Platonic arguments for the philosophic life as a solitary and divine life of pure intellect as dubious, because these arguments contradict what Aristotle teaches in Books 8-9 about the natural sociality of human life and the primacy of friendship as rooted in human biology.
The philosophic life does appear in Books 8 and 9. But here it appears as activity that is cultivated by friends as a social activity of those who find their deepest existence in philosophizing together with their friends. By contrast, the word "friendship" (philia) never appears in the Platonic account of philosophy in Book 10, which depicts philosophy as a life of god-like solitude separated from social life. The only concession to social activity in Book 10 is that the philosopher is said to perhaps benefit from having "co-workers."
In Books 8 and 9, philosophy as an activity of friends is activity of embodied minds in social interaction, which can be explained biologically as an activity of human beings as rational and political animals by nature.
And while Book 10 suggests a dominant end conception of the human good, in which all goods are ranked below philosophy, Books 8 and 9 suggest an inclusive end conception of the human good, in which philosophy is one good among many. The thought here is that different human beings will rank the natural human goods in different ways to conform to their natural temperament and their social circumstances.
At the end of his account of friendship, Aristotle writes:
Is it then the same way with friends as with lovers, for whom seeing the beloved is their greatest contentment, and the thing they choose over the other senses, since it is especially through seeing that love is present and comes to be present, so that for friends too, living together is most choiceworthy thing? For friendship is a sharing in common, and one has the same relation to a friend as to oneself, while in relation to oneself, the awareness that one is is something choiceworthy, and thus it is so in relation to the friend as well; but the being-at-work of this awareness comes about in living together, and so, naturally, friends aim at this. And whatever being existence consists in for any sort of people--whatever it is for the sake of which they choose to be alive--this is what they want to be engaged in with their friends. This is why some friends drink together, others play dice together, and still others engage in athletic exercise together and go hunting together, or engage in philosophy together, each sort spending their days together in whatever it is, out of all of the things in life, that they are most contented by; for since they want to share their lives with their friends, they do those things and share those things that they believe living together consists in. (1171b29-72a8)
One can see here why Douglas Rasmussen and Douglas Den Uyl look to Aristotle's study of friendship as supporting their Aristotelian defense of liberalism. It seems that although the generic goods of life are universally the same for all human beings by virtue of their human nature, the ranking and organization of those generic goods is individualized for the life of each human being. Moreover, this pluralism of good lives is cultivated in civil society, where moral character is shaped through natural and voluntary associations.
Some related posts can be found here, here, and here.