Piracy would certainly be profitable, but it's high risk for the high reward and I imagine there will be other drawbacks.
Pros:
- Unlike regular traders you don't have to pay for cargo, so any you attain is almost pure profit aside from the cut the fence gets. While selling in the ideal system like a trader would might maximize profits, you certainly could just sell it immediately to do more pirating quickly.
- There's something awfully romantic about being a pirate, isn't there?
Cons:
- Difficulty in entering civilized areas. The cops want you dead.
- Purchasing new ships and equipment from pirate stations may come at a premium, what with "reputable" manufacturers not directly selling there. Shipping and handling fees may apply.

- You'll probably be in combat more frequently than most traders, so there's the pesky repair bills.
- Most non-criminals want you dead and many are motivated enough to try. Some might succeed.