After two years of immense prosperity, the last year has been a disaster for the Somali pirates. For example, in the last eight months, only six ships have been captured, compared to 36 ships in the same eight month period a year ago. Pirate income is down 80 percent and expenses are up. Pirates have to spend more time at sea looking for a potential target, and when they find one, they either fail in their boarding efforts (because of armed guards, or better defense and more alert crews) or find anti-piracy patrol warships and armed helicopters showing up. Unlike in the past, the patrol now takes away the pirates weapons and equipment, sinks their mother ships and dumps the pirates back on a beach. The pirates claim that some members of the anti-piracy patrol simply kill pirates they encounter on the high seas (some nations have admitted doing this, at least once, in the past). But no one does this as official policy, and the rules are still basically "catch and release." The big change is that the patrol has become much better at detecting pirates, on captured fishing ships, and shutting these pirates down. Often the pirates bring along the crew of the fishing ships, to help with the deception. But the patrol knows which fishing ships have "disappeared" and quickly identify those missing ships they encounter, and usually find pirates in charge. The anti-piracy patrol also has maritime reconnaissance aircraft that seek to spot mother ships as they leave pirate bases on the north Somali coast, and direct a warship to intercept and shut down those pirates. The pirates have been losing a lot of equipment, and time, and money needed to pay for it.
I don't like the idea that there's a "tolerable" level of piracy, but that seems to be the most pragmatic course available.
The bottom line is that the pirate attacks, even if they took two or three times as many ships in their peak year, would not have a meaningful economic impact on world shipping. Total cost to shipping companies (ransoms, extra fuel, security equipment and services) is over $10 billion a year. For example, the international anti-piracy patrol in the Gulf of Aden costs $500 million a year, a fraction of a percent of the defense budgets of the nations involved. Politicians and bureaucrats can stand that kind of pain, and will likely do so and refrain from doing anything bold in Somalia.
Decisively dealing with pirates would necessarily harm civilians as well, and no one wants to get branded as a war criminal. So, the piracy continues.