Well, first of all, it wouldn't be "rape", in any case.
Second of all, if any girl constantly harrassed them over the computer and sent them tons of E-Mails saying "Have sex with me or your a loser!", it kind of interferes with any rational thought process.
And it isn't a reasonable situation to present a person with.
Entrapment is whenever the state causes you to commit a crime by their own, personal means, often with exxagerated or ridiculous situations presented to the "criminal" - it's not a policing tactic that I would prefer to allow. These guys had no intent to molest children - the point is, the "state" found them, harrassed them, and caused them to commit the crime.