Paddy, this isn't about the FBI posting bogus links, it's about someone outside of the govt posting disguised links for the express purpose of sending unsuspecting rubes to the FBI sting site. All it takes is for one person to discover the link without getting busted and sharing the info with others.
As a trick, it is common as dirt. It was pretty common on Slashdot.org back in the late 90s to post an innocent looking link that actually took you to
www.goatse.cx. Google that if you feel brave.
The article plainly said the FBI isn't checking the referring sites. That means they don't care how you got there. It could be a link to Kiddy Porn or a link to Blueblocker sunglasses. All they know is you got there somehow and they're going to raid your home.
Here's another way for an internet bad guy to use this as a weapon against rubes: register a common typo version of a legit site, say www.a
mredpolitesociety.com and set it up with a redirect to the kiddie porn site the FBI is running. You tried to get to APS, but fat fingered the url, now you have the FBI visiting your house. As the article said, they don't check the referring site to ensure you actually wanted kiddie porn, they only care that you ended up on their site.
Chris