Rather than the interpretation that Jethro is a classic narcissistic psychopath and budding dictator (as some critics have concluded) who actually wants to conquer the world JUST BECAUSE…that's what these mutants do after all...here are a couple of alternative possibilities…
This is a story about characters who are intending to live "forever" and undoubtedly some of them will live quite a long time and their adventures will be recounted in subsequent sequels. At the beginning of the story, Jethro is a twenty-something philosophy student, and later, a graduate. He spends several years sailing around the world while absorbing the contents of 500 books and then towards the end, virtually the ENTIRE cannon of transhumanist thought that was provided to him by a leading, and much more seasoned, transhumanist.
He is in the formative years of the development of his personal philosophy (a virtual embryo for a being who might live hundreds or thousands of years). He is forming the premises and conclusions that he deems to be necessary to achieve his immediate goal: NOT DYING. He envisions that some people may take actions that will impede or completely block his movement toward that goal. He decides, therefore, that the more personal power he can accumulate, the better chance he'll have to be triumphant against people who want to thwart his goal-directed efforts.
Now, being a young man, with a young man's passions and energy, not to mention, HIGH TESTOSTERONE LEVELS, he quite naturally couches his embryonic philosophy in forceful, in-your-face, uncompromising Nietzschean-esque, "Jethro The Conquerer terms." However, when push comes to shove, in the real world, he doesn't implement all that is mentioned in his most belligerent rhetoric.
One reason for this could be because of a strategy, which is foreshadowed more than once in the story and that is: Jethro views military conflict between the transhumanists and the rest of the world to be inevitable and he would rather get it over with sooner rather than later so he and the other transhumanists can get back to their life-extension research because they are all in a race against a heretofore unavoidable death-clock.
When comparing Jethro's words vs. his deeds, it is extrememly important to take notice of the fact that the transhumanists don't actually take any actions to precipitate each successive escalation of planned and actual violence by the coalition of war-mongering governments plotting their destruction. Rather, at each turn, it is only Jethro's uber-forceful/scary words that frighten the world powers into aggressive action. We don't know for sure if Jethro is just being his natural, "charming" self when he makes these beligerant statements or if he actually may be laying it on a little extra thick in order to incite his adversaries into action so that he can justifiably retaliate forcefully and decisively in self-defense.
Jethro is nothing if not brilliant, and unless he really is a psychopath who may be somewhat clueless to others' emotional reactions to such things (which is not borne out by his interactions with the people closest to him), he HAS to understand how his Genghis Knights MIGHT-MAKES-RIGHT Barbarian Overlord schtick will be received by the "unwashed" and already fearful masses.