I'm sorry, but "Hagrid is lonely" is not a concern worth five seconds of thought when Harry could be working on getting rid of dementors or Azkaban or Death Eaters or death.
This is a nonsensical statement. It's not as if Harry was using up those five seconds, or five minutes for any of those concerns.
Harry was just being a little jerk.
But actually befriending Hagrid is a decision that would take up a considerable amount of Harry's time.
Harry's only human, he can't devote all of his free time to saving the world. He needs intellectual and emotional cooldown time. But Harry's also an introvert. Spending social time with people he doesn't relate to is not cooldown time for him, it's something he'd need cooling down from. That being the case, being friends with Hagrid would eat into Harry's productivity time. It's a transparently bad move, and he doesn't have to spend five seconds considering it in much the same way that a competent chess player does not spend five seconds considering whether to checkmate himself.
Update: Discussion has moved on to a new thread.
After 61 chapters of Harry Potter and the Methods of Rationality and 5 discussion threads with over 500 comments each, HPMOR discussion has graduated from the main page and moved into the Less Wrong discussion section (which seems like a more appropriate location). You can post all of your insights, speculation, and, well, discussion about Eliezer Yudkowsky's Harry Potter fanfic here.
Previous threads are available under the harry_potter tag on the main page (or: one, two, three, four, five); this and future threads will be found under the discussion section tag (since there is a separate tag system for the discussion section). See also the author page for (almost) all things HPMOR, and AdeleneDawner's Author's Notes archive for one thing that the author page is missing.
As a reminder, it's useful to indicate at the start of your comment which chapter you are commenting on. Time passes but your comment stays the same.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: