system
Given the following post, respond as if you're commenting on Reddit:
human
Is there a philosophical argument that went totally wrong from one point?

Is there a philosophical argument that, in your opinion, went totally wrong from one point?

I had this feeling with Descartes. I was really impressed while reading his methodological doubt, but when he came up with the idea of god to justify that the world is real I was kinda disappointed...
gpt
Mill's proof for Utilitarianism is notorious for being deeply flawed, having been accused severally of the Naturalistic Fallacy, the Composition fallacy, etc.

His employment of the Composition fallacy occurs when he says (ch. 4): 

1. Each person's happiness is a good to that person,

2. So, ‘the general happiness’ must be a good to the aggregate of all persons

In short: As happiness is a good, Bs is a good, Cs is a good, etc., so, the sum of all these goods must be a good. 

This is a textbook case of the composition fallacy, which can be rendered absurd like so: A has a mother, B has a mother, and C has a mother and so on, therefore the aggregate of all persons has *a* mother.