In a sting like this, LEOs pose as underage boys or girls online and sexual predators are caught. People who are not online looking for underage children to have sex with will NEVER be caught in a sting like this.
Entrapment (as you noted) occurs when LEOs approach citizens and coerce them into committing crimes they never had any intention of committing.
The libertarians simply believe that ANYTHING law enforcement does to interfere with their sexual urges is somehow unconstitutional.
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Yes. Or any other urges.
That's a pretty broad paint brush you are using.