debate

It implies that book alien does not think the debate would be entertaining so the debate would be about if the debate was entertaining. It’s a similar concept to the Monty Python “I came here for an argument” skit where the argument ended up being on whether being contrary was the only need to have an argument.

In my opinion, the alien in the right pulled a fast one. He set up a joke. When the left alien asked if he thought a debate would be fun, the right one said “in my opinion.”

It doubles as both an affirmative—“yes it would be fun”—and as an inconsequential opinion which is the start of an argument or debate.

That’s why the alien on the left points at the other. As if to say “ah I see what you did there!”

Edit: ah notice the little smile and the sneaky squinting eyes on the alien to the right in the final panel. So smug that he made a funny 😆

Alien on the left is about to debate whether or not that would even be entertaining. The point of the comic is that debating our opinions with each other is stupid because they don't matter and it's not even fun.