It sounds just like Albus.
- He knows Harry must one day defeat the Dark Lord.
- He knows that the Dark Lord is alive and someone or something is drinking unicorn blood.
- He knows the trio (or more likely just Harry, the other two are a bonus) must get to the Mirror of Erised, past Fluffy.
- He knows Harry is being bullied by Malfoy.
- He knows that unless he toughens Harry up, he has no chance.
The whole experience, with the centaurs, the unicorn blood, hearing about Fluffy (which may have happened earlier, but lets assume Albus wants to be sure Hagrid blabbers), seeing Quirrel, seeing Malfoy run, was intentional.
It's almost as though Albus is the greatest (and craziest) wizarding genius the Wizarding World has ever seen.
Yes, it's for the sake of plot, but Albus knows what plot he wants, knows the prophecy and is helping things along.