Almost every table in every database I've seen in my 7 years of development experience has an auto-incrementing primary key. Why is this? If I have a table of U.S. states where each state where each state must have a unique name, what's the use of an auto-incrementing primary key? Why not just use the state name as the primary key? Seems to me like an excuse to allow duplicates disguised as unique rows.
This seems plainly obvious to me, but then again, no one else seems to be arriving at and acting on the same logical conclusion as me, so I must assume there's a good chance I'm wrong.
Is there any real, practical reason we need to use auto-incrementing keys?