In some countries just conspiring to commit a terrorist act can lead to a conviction, so in a way you can say that FBI is 'forced' to operate this way to get a conviction for a would be terrorist.
And given that their powers are so broad and immense, we rely on them acting in good faith and morally (we must, because we have nothing else), so we criticize them when they do not do that.
Preying on mentally ill Muslims and concocting elaborate schemes which exploit their inability to function normally to trick them into "taking part" in (sometimes little more than just 'agreeing to') some sort of plot that doesn't exist and then patting themselves on the back for "getting a terrorist" and locking the mentally ill person in jail for decades is, well, sick, and not a shining example of 'acting morally', so the criticism is well-deserved.
That said : "Of 508 defendants prosecuted in federal terrorism-related cases in the decade after 9/11, 243 were involved with an FBI informant, while 158 were the targets of sting operations. Of those cases, an informant or FBI undercover operative led 49 defendants in their terrorism plots, similar to the way Osmakac was led in his." So now 49 cases out of 508 were 'led' by the FBI, not clear how many of those had to do with mentally unfit individuals or if Osmakac was the only one.
One of those countries would be the US: conspiring to commit any federal crime is, itself, a federal crime [0], and the US federal terrorism statute (which only applies to acts outside of the United States, though acts of terrorism within the United States are covered by other criminal statutes) also especially criminalizes attempts and conspiracies. [1]
[0] 18 USC Sec. 371; https://www.law.cornell.edu/uscode/text/18/371
[1] 18 USC Sec. 2332(b); https://www.law.cornell.edu/uscode/text/18/2332
Like the US
For example, this dude got convicted for 'conspiracy and other offences' after his buddies were 'firing assault rifles at security personnel and law enforcement officers' and ended up getting killed.
https://www.justice.gov/opa/pr/phoenix-man-convicted-conspir...
or the Al-Arian case: https://en.wikipedia.org/wiki/Sami_Al-Arian
Not to mention things like '...20,000 hours of dialogue from 472,000 wiretapped telephone conversations on 18 tapped lines gathered from 1994 to 2003', multiple court appearances etc etc.
This just goes to demonstrate exactly why FBI is doing things the way the article describes.
That's not enough. The FBI has to completely operate within the framework of the law, just like any other law enforcement agency.
their actions can later be deemed to be lawful or not depending on whether their perception is justified.
for example - the use of lethal force has to be justifiable (this applies to everyone not just the FBI obviously), one's justification after the fact can be considered valid or not depending on circumstances.