Kick Kennedy described the event as "normal" in an interview with Town & Country all the way back in December 2012 – years before her father ran for office.
You just asked me for the answer, so in this case, you! Your second sentence does imply that you are, as the "not even X, let alone Y" implies that to reach Y you must pass X.
Please answer the question: Why is it ethically neutral to intentionally expose a child (he wasn't passing by, he found out it happened and drove there with his daughter) to such things on a day-to-day basis?
Its not my onus to answer that, that's akin to trying to prove a negative. As the one making the claim, you are supposed to try to prove it. How is exposure to a whale carcass unethical?
Because exposing children to traumatic things can cause psychological issues and watching someone carve up a whale with a chainsaw is pretty damn traumatic for a normal child.
Although legality and ethics do not always coincide, they often influence each other. Many laws are based on ethical principles, such as the protection of human rights, wildlife, or the environment. They reflect a societal consensus that actions that violate these principles are both unethical and should be illegal.
In this case, RFK Jr. most likely violated several laws like the Marine Mammal Protection Act (MMPA) and the Endangered Species Act (ESA) which make it illegal to disturb, remove, or possess any part of a whale, even if it's dead, without a permit. This is not "normal" behavior.