The bottom line, if you swim enough in the ocean, you will probably eventually get stung, cut, or bit. There is a lot of life in the ocean. If you can't manage the risk, swim in the pool.
For what its worth, I've been swimming in various oceans about 10 days a month for over 10 years. I've been stung by jelly fish several times, bit by crabs, nipped at by small hungry fish, cut on sharp rocks and coral (once, serious), stabbed by sea urchins (I stepped on one), and almost monthly I get coated in this stingy chemical that's released by some plant when the currents are right and they get tossed about.
I've had the crap scared out of me as I was chased on a jet-ski by a school of sharks (they turned out to be dolphins, but they scared the hell out of me until I figured that out). None of these things would keep me from going in an ocean. I've had more accidents on dry land than in the water (nicks, cuts, scrapes, even bone breaks, etc.) and the closest I've ever come to breaking my neck was when I slipped on a pool deck.