Why does Gandalf hate Pippin?

Gandalf knows that Gollum is not entirely evil. There is still the good "Smeagol" side to him. Even though he is very wise Gandalf cannot see the ultimate fate of the Ring, but he senses that Gollum will have some part to play for good or evil, so, like he says, "the pity of Bilbo [and himself] may rule the fate of many."

Also, Gandalf is not the type of person who will kill recklessly. And he himself, good and powerful though he is, has been tempted by the Ring's power, so he can vaguely understand Gollum's misery. Gandalf is very much like Jesus, who was tempted by Satan and can understand, though not agree with, a human's lust for power and easily corruptible heart.