But it doesn't actually curb piracy! Like other DRM, it's touchy-feely pointy-haired-boss crap. "Let's have a central authorization scheme! People will get an ID from their serial key, and that way we can lock down the whole system! You can't join a game or download updates without being logged in!" So regular users have this hoop to jump through, with this bloated memory hog running when they want to play, get flaky errors in game or with components like the friends list when the ID server messes up, or at times like tonight (or however long) just can't use their purchased product at all. Meanwhile, the pirates immediately hack the program to avoid the login, and play on hacked servers that don't require a Steam ID, and take updates from a single legal copy and hack to as many copies as they want.
And no, you don't want Steam. You may want a program with similar goals for program maintenance and purchasing, but Valve's actual implementation is terrible.