What are general and specific purposes for satire?
Generally, satire shames people who do wrong; specifically, it shames powerful people who do wrong.
Historically, there have been two flavors of satire: Horatian, which is kind of gentle and "Just kidding, Frank!" in its intent, and Juvenalian, which is a bit more unflinching. Horatian (named for the Roman satirist Horace) takes a wide view of the failings of all mankind. Juvenalian (named for the Roman satirist Juvenal, who famously asked "Who watches the watchmen?") is a little more brutal in intent and effect, and usually targets those in positions of privilege and power.