I'd go philosophical : Alternate History and idealisation.
I - Utopia as the root of AH
Introducting the subject by pointing out the immemoriality of idealized situation. "Once upon A time", etc.
Pointing out that the appearance of Uchronia is tied up with the rationalisation of the world, when History cease to be moral to become a science, forcing the marvellous and utopic to take refugee, still in another far time, but an unrealized time.
Using the first known AH books to highlight this (read some short extracts, points illustrations or maps, etc.) :
- Napoléon et la conquête du monde, 1812-1832. Less a wisfhul thinking and a wank, a plaid for the napoleonic political conception that while failed historically, remained legit as well in French politics and introducing it as victorious providing an exemple of this legitimacy
- P.'s Correspondence : A belief in the deep decline of individuals. As people change everyday without noticing, he takes people that died in glory and famed, and make them lives on for we see their fall.
- Uchronie, or the "history how it should have been" in order to prevent untolerance and religious wars.
etc.
II - Alternate History as a mirror.
These different worlds depictions have all one point in common, our world, our reality.; as we wrote them trough smoke.
The most obvious, and caricatural, outcome is the "evil beard" universe a la Star Trek. The role is to point out how, eventually, we are good and how it could be really worse.
Or the reverse, with for exemple the comics Luxley, with Natives invading Europe, inflicting on us the same treatment that we did (only to prevent their own doom). Here, cries of innocence from Europeans takes all their tragic : they are, these ancestor that never been, but our real ancestors weren't.
Idealisation works on both ways, and eventually AH serves as defining ourselves trough time-playing, as many futuristic science-fiction.
There, search for several better known media, and introduce less known AH.
Conclusion being about how, questioning and entertainment aren't opposed (highlight the use of AH tropes in Science-Fiction), but how they participe to each other, as in any good science fiction.