I have no part of me that says this is awesome. It's disgusting and wrong. Pirates are scum, and deserve to be shot at. However, no one should derive such joy that they would opt to spend their leisure time killing other human beings.
Problem #1: Overzealous pirate hunters may kill people who are not pirates.
Problem #2: There are tactical questions involved in any preemptive military strike, which is what this amounts to. Not only could it fail to reduce piracy, but it could make it easier to recruit more violent pirates who will begin a campaign of murdering ship crews.
Problem #3: One must wonder whether it is just to kill a person who, although intending to pirate a ship, has yet to commit any crime. Such a scenario is not unimaginable when non-experts are leading death-tourism groups after alleged sea pirates.
Really, I could go on. How are you not seeing the problems with this?