Not only can I see why someone might
intentionally create a cursed item, I rather like the idea that magic item creation can be botched.
I don't think every curse should be critical. In one
3e adventure, I included a scythe that was possessed by its former (tall albino) owner. It gave magic bonus, but the person who used it grew slowly over time until he reached 7 ft, and his skin paled to albinism. The PCs found it in the hands of a tall, pale goblin. It freaked them out so much that they chose not to use it.
I quite like the sword that desires to draw blood before it is sheathed. It has power, but if you draw it "just in case" it tries to take a hit point from you before you can sheath it again.
I like the idea of items that offer skill ranks.
Earrings of Swimming 8 ranks, for example, appear as tiny jade fish that, when worn, grant the wearer a Swim skill of 8 ranks. Not +8 ranks; 8 ranks. If you have fewer ranks, it is a boon. If you have more....not so much of a boon. A character with 10 ranks of Swim who wears these earrings has 8 ranks until he takes them off.
My crypt with the dread ghoul mouse swarms contained a circlet that, among other things, attempted to possess its wearer so the long-dead reptilian sorcerer whose circlet it was could live again.......
Anyone who is a fan of
Doctor Who,
Torchwood, and/or
The Sarah Jane Adventures can easily bring to mind episodes that, essentially, deal with cursed items.
RC