Hunting them is POINTLESS! In this case, nature will balance itself as it always does and remember people - it really is just one big ocean.
With all due respect this mentality is exactly how we get ourselves into these situations....see the slug example above. If Nature, God, Allah, Buddah or whoever had intended for lionfish to be in the Atlantic he would have put them there. Most likely he would have also placed a few natural predators in too. Nature will not take its course because WE have already messed with Mother Nature. Granted that a strong grouper population may help to control the lionfish but how much damage do we allow the lionfish to do to reef fish populations in the interim. Bear in mind that the Nile perched eradicated over 200 species of fish in Lake Victoria.
Also, there is a contradiction in the "don't kill them" logic. That logic says it is OK for grouper to wipe out the lionfish but man can't help. There is no difference. In the natural balance of nature I would agree that man changes the balance of nature but in ANY case where we are dealing with an invasive species introduced by man nature has already been upset and MAN has the duty to try to reset the balance. If the grouper can kill the lionfish then I think man should do all it can to help the grouper out.
We should also do it quickly before the only fish left to see on the reefs of the Caribbean are lionfish. But don't take my word for it read this article and hear it from the experts.
Here are two excerts from the article linked below.
"New studies headed by Mark Hixon of Oregon State University are about to be published in a peer-reviewed science journal found one lionfish can deplete 79 percent of a reef in just five weeks. That means coral ecology dies and algae takes over."
"You know the potential is there for it to be devastating," said Tom Jackson with the National Oceanic and Atmospheric Administration (NOAA).
Deadly lionfish invade Florida waters? : Fishing & Boating : TCPalm
Just my two cents....
By the way...as with most non-native species there are no fish and wildlife regulations that apply to lionfish, unless they are in a sanctuary or park where everything in the park is protected. As such you can spear, kill, club or otherwise all you want.