There being a market for something does not justify its existence, at least morally.
In the case of a Safari, there is this moral middle ground - according to the countries policy, if an animal attacks a human, it generally is a candidate for being put down because of perceived danger to humans in the area, but on the flip side, its also morally wrong to kill an animal just because it does that.
In the case of the gang warfare, you are doing a service by reducing the number of gang members and crime, but its also morally wrong to take someones life in offense for personal entertainment? (If its not clear, the difference in doing that in PNG versus any other country is because specifically of the lack of law enforcement that is the way of life there)
Another hypothetical scenario - say you have a country where age of consent is low, and certain type of porn that is highly illegal in the rest of the world is freely available (which is not far from reality, scarily). You can't stop the creation or distribution of that porn without basically invading the country and changing its law. However, what if you used said porn and supplied to convicted pdf files in your home country so that they are less likely to exploit young kids irl? Is that morally wrong, or is it morally justified?
Lets say that you have a country where slavery is legal. The slaves of course don't like it. But lets say that the populace is largely in favor of it, because slave labor keeps the barebones economy going and people can trade and have food to eat. Most people don't actively capture slaves, they just buy them at the market.
If you had the power to eliminate slavery in that country, you would free the slaves, but you would basically condem a lot of the people to die from starvation.
So whats the "correct" moral stance? Real world isn't black and white like you would want it to be.