I think the point is that the person is willing to do something drastic when presented with the opportunity. Instead of the sting providing that opportunity, what it if was some group? How can you be sure that there would not have been a crime?
I don't see any perversion of justice. Don't want to end up in jail? Don't commit a crime .... regardless of who provides you the opportunity to do so.
People don't generally have such opportunities - you think it's a common opportunity to have an easy path to robbing 20 kilos of cocaine from a large drug dealer? "Hey, all we have to do is x,y,z, and we'll each have half a million dollars."
If Mila Kunis or Emma Watson or whichever actress is a favorite of yours, came up to you out of nowhere in a bar, without you even attempting to make contact with her first, and said, "hey, give me $10 to go buy a drink and we'll head upstairs and have sex" - Are you going to respond to her, "I'm sorry, if I gave you cash in exchange for sex, that would be illegal." No, you're going to jump at the opportunity. And, after exchanging the $10, the vice squad sweeps in and arrests you, leading to a post, "I was set up! It was entrapment." You weren't out looking for a prostitute; you might never look for one in your life. But, when a very attractive one comes up to you and offers an extremely attractive price; as someone said above, everyone has their price. And, that's long been regarded as entrapment.
So, for a long time, it's been: beautiful woman (police officer) comes up to you and offers to perform services for a fee; if you say yes, it's entrapment. The men who were released were walking the streets looking for robbery partners. They weren't putting ads in papers, visiting websites looking for crimes to commit - they were solicited in a way that's no different than the unconstitutional type of prostitution stings. Instead of offering pleasure for money, they're offering money in exchange for other illegal activity.