Why must Harry leave familiar Hogwarts territory before facing Voldemort? And why would he be safe over the summer at the Dursleys?
A traditional motif in folklore is the requirement of the hero to leave his own home grounds before facing the dangers of the unknown. Each of the books in this series finds a way to remove Harry from the safe confines of Hogwarts and pit him against a dangerous adult wizard. Harry does not know where he is or how to provide himself with protection. All of the final battles are slanted against Harry to due this removal from Hogwarts, and therefore when Harry triumphs, we know it is out of his own gifts and courage. The Dursleys are able to protect Harry because members of the same family, whether they like each other or not, have deep bonds that allow them to provide some safety for each other. Harry and Voldemort, for example, cannot attack each other because their wands are referred to as "brothers." Once Harry is within the realm of his Muggle relatives, he is likewise protected.
Is Hermione correct in her crusade against poor living conditions for house- elves?
Even though house-elves are characterized as servile and community-oriented, Dobby manages to negotiate paying terms for a job at Hogwarts. He shows that it is possible for house-elves to take initiative by standing up for his rights, even in minor, tittering ways. Hermione is right, to a great extent, although it must be noted that creatures of different breeds have different qualities that must be addressed and reacted to, not ignored.
Why do Voldemort's victims return to help Harry?
The return of these ghosts reminds Voldemort of the consequences of his past decisions, and allows them to leave their mark on the living by prohibiting more people from dying their death. Harry escapes only because the ghosts of Voldemort's past victims arrive on earth to torment their murderer and protect other possible victims. Voldemort extinguished each of the people who return as shades to protect Harry, and each of them has a power that Voldemort does not have—they cannot die again, but he can. His killing curse dictated their fate, yet they are not gone from this world, and they can still affect the lives of others. As he hurt them, they will try in turn to make his life difficult.