He simply cannot see a mechanism whereby the advantaged English-speakers would generally consent to learning it. Therefore access to power in the world continues to be through English, until the next revolution, peaceful or not.
I'd like him to consider this mechanism: English speakers compete amongst themselves. Being monolingual in English trumps being monolingual in anything else, but it is still a disadvantage, compared to English plus something. This could be the key to making the unrealistic practical.
The scale of the monolingual English disadvantage is not such that it often inspires whole-hearted, serious investment in languages education, but the advantages of bilingualism can usefully be split into general advantages, and advantages relating to specific languages. The first catagory can be economically and effectively delivered through integrated Esperanto instruction in primary schools, allowing time to choose which national language seems most strategic for particular students later.( For comparison, we already teach primary kids "science" and senior secondary students "physics" and/or "biology' etc)
English speakers do not have to be broad-minded, or selfless in any way, to make such a rational, economical choice for their children.
And if they do, the next generation might reasonably be more open to wider use of Esperanto, as a language that they have anyway and that, incidentally, other global citizens can learn in a fraction of the time that English was demanding.