> On the other hand, any departure from a pure interpretation of the law is very dangerous
You should read the law in question. This would be Section 107 of the Copyright Act, which defines "fair use". It's extremely vague and is best interpreted as a set of considerations that the courts should take into account so that they can handle situations like this one on a case by case basis. If Congress wanted to be more prescriptive, they could (ETA: and if they become unhappy with the courts' decisions they still can in the future), but I think that would lead to worse outcomes.
You should read the law in question. This would be Section 107 of the Copyright Act, which defines "fair use". It's extremely vague and is best interpreted as a set of considerations that the courts should take into account so that they can handle situations like this one on a case by case basis. If Congress wanted to be more prescriptive, they could (ETA: and if they become unhappy with the courts' decisions they still can in the future), but I think that would lead to worse outcomes.