Usage of 'Ikenai'

Does the last sentence meant the author felt strongly that we should protect the beauty of Japan’s four seasons?

Why is mamoranakute followed by 'ikenai" (which has a negative expression)?

Welcome to the labyrinth of expressing “must” in Japanese^^
Here’s a pretty helpful guide: Expressing “must” or “have to” – Learn Japanese

The logic behind the structure is more or less “if this is not done, it’s not good”. In your example, literally “not protecting does not go.”
It takes some time to get used to^^

「迷宮」という表現は面白いですね。私にとっては、英語の語法や文法がそれです。時間をかけて慣れていかなければならないという意見に賛成です。