With the CFAA in the USA it's not so much, "What is illegal and am I breaking the law?" because the answer is always, yes, you're breaking the law. Everyone violates the CFAA's many provisions multiple times per week.
The real question is: have you rocked the boat enough to get slapped down for it?
There are lots of reasons why JavaScript might not be executed, ranging from accessible browsers to privacy concerns.
Morally, yes — You know the intent is not to share that content and you are deliberately circumventing the mechanisms to prevent access. I think about corner shops which have produce outside. It's obviously there for sale, but you can easily walk past and grab an apple without any intervention. The fact that they haven't instituted a complicated security system doesn't mean you are morally free from your actions. (I think it is fair to equate physical property with intellectual property in this case)
Legally, I think "no" — at least, I don't think it's been tested in court — but I can also draw a line to a "yes." If a court were to hold that a site's terms and conditions prevent you from accessing paywalled content, and you do so anyway, the argument could be made that you have intentionally accessed information without proper authorisation. But, its intellectual property, as long as you don't store it or re-transmit it, it would be hard to argue you saw it in the first place. Since it's already in the payload, it does raise an interesting question as to whether it was "accidentally/unintentionally disclosed." If someone sends you IP by accident which don't own, you don't suddenly get rights to it...
Of course this is absurd, but just because its easy to circumvent doesn't mean you didn't circumvent it. The CFAA can be interpreted quite broadly...
The site developers should add a better paywall if this is a serious concern