We don't know too much about the speaker. We don't know how tall he is, what color his eyes are, whether he is a cat person or a dog person, where he grew up on went to school. We do not know the very basics about him.
But we do know two things: one, he's always up for an argument (even with an eight-year-old) and he has a pretty limited view of death. For our speaker, once you're in the ground, it's sayonara, suckers. Our speaker's gonna delete your email from his contact list, maybe even burn the old photos that you took together. This guy believes that death is the end of everything. And he believes it so firmly that he's willing to argue with a mere child.
Now, it may seem weird to use a crotchety old grump for a speaker, but that's actually part of Wordsworth's genius. Our speaker's the perfect foil against which plays the endearing persistence of the little girl. She's all the more bright-eyed and fervent for the grim pessimism of our speaker, who seems to be there just to show by contrast how thoughtful and committed this little girl truly is.