Why Dobby? Of all the characters she could have killed to motivate Harry to unravel the mystery of the horcruxes and stop wasting time with the Deathly Hallows, Dobby would have been one of my last choices. I was certain Ron was toast. He was the one character closest to Ron, in age, in interests, in friends. Ron was Harry's surrogate brother, the closest thing to family he had at Hogwarts. If Ron was killed, Harry would have no choice but to seek revenge.
But revenge is not a noble pursuit, and if anything Harry is a noble character.
That leaves Arthur Weasley or Hagrid. Both played the role of patriarch to Harry. Anyone wanting to be a father-figure to Harry was doomed. James, Sirius, Dumbledore all died trying to save Harry from a similar fate. Arthur and Hagrid were surely in line, yet they were able to survive the deadly Battle of Hogwarts.
I have a hard time accepting that the death of Dobby was enough to change Harry's outlook and pursuit.
Dumbledore in limbo. Rowling had a great opportunity to explain many of the mysteries in her books in one chapter, when Harry meets Dumbledore in limbo and with that whimpering specter of Voldermort's splintered soul shivering in a corner. She could have explained how James and Lily died; why Harry was able to survive; why Sirius was so attached to James and not able to see Harry differently. She missed her chance to explain much of how Harry became the Boy Who Lived.
Journalists. Rowling hates them. At least her portrayal of journalists in her books is far from flattering. Rita Skeeter is a metaphorical and literal pest. The Daily Prophet is filled with more rumor than fact and Rowling relies on the interpertations of Hermione to translate the stories into anything credible. The Quibbler is a joke of a publication. And Xenophilius Lovegood, the publisher of The Quibbler, is a treacherous traitor.
Harry. Even though the books are named for Harry Potter, by the end of The Deathly Hallows, it becomes clear he is a fairly inconseqential character. Severus Snape is the catalyst for the stories, not Harry. Snape is duplicitous, yet incredibly loyal to Dumbledore. Without Snape, the powers of evil probably prevail. Snape sacrifices his life so those loyal to Dumbledore have a chance to rid the wizard world of Voldermort's evil. Harry just happened to be the unfortunate soul who embodied the extent of Voldermort's arrogance. If anything, Harry was a convenient distraction so Dumbledore and Snape could come up with a strategy to defeat Voldermort.
There is no way we will be able to ask all of these questions. We will probably be lucky to ask one or two. And we probably won't get any sort of detailed answer.
But it's not going to stop us from asking.