The whole point of Hinduism is for the Atma to return back to the Paramatma, so Samsara is literally an obstacle to the end goal. General Good and Bad may be human constructions, but specifically Dharma and Adharma have been determined in sacred texts (Vedas, Upanishads etc.), of Hinduism and by countless of Rishis. And that adhering to a dharmic way of life, being indifferent to Sukha-Duhkha, and pursuing the knowledge of Atman will result in Moksha.

What you're saying may apply to Buddhism, but not Hinduism, because words with the same name such as Karma doe not mean the same in Buddhism as they do in Hinduism due to disagreements of the two dharmas.