This is a post by Lars Avermarie, which I fully support and agree with.

I would argue that any attempt to “correct” posture is assuming blindly and is begging the question that we:
1. That we know what “normal” is! We need that to be able to say something is “abnormal” and needs “correction”. To be able to do that, we need “normative data”.
“Normative data is data from a reference population that establishes a baseline distribution for a score or measurement, and against which the score or measurement can be compared.”
Ref.: Campbell 2013
The normative data we have, stat that posture is “highly variable in different individuals”, and Stagnara et al concluded that the “span of possible values of maximum kyphosis and lordosis in subjects with no spinal disease is considerable. . . It is therefore unreasonable to speak of normal kyphotic or lordotic curves” Roussouly et al.
When talking about human movement and posture, variability is the norm! Movement and posture are like fingerprints. Trying to “correct” a posture into an imaginary and made-up metric (norm) that has no validity is like trying to “correct” a person’s fingerprint!
“One of the most common features of human movement is its variability. Human movement variability can be described as the normal variations that occur in motor performance across multiple repetitions of a task (Stergiou, Harbourne, & Cavanaugh, 2006). This variability is intrinsic in all biological systems and it can be observed quite easily. If a person tries to repeat the same movement twice, the two actions will never be identical.” Stergiou et al. 2011
2. It is also begging the question, that we in fact, can “correct” posture! This has not been shown. Posture is influenced by multiple factors like age, state of mind, cognitive load, and a large degree of inter-individual variability.
The belief about “abnormal” posture causes pain as a single factor, not solid science. It is mostly our education tradition and culture that maintains this assumption about some “normal” or optimal posture, an imaginary sort of “ideal” posture. This notion of one single “normal” posture; is more based upon a cultural construct and biomedical and biomechanical beliefs, not the repeated assessment of the validity of these assumptions and beliefs.
The fixed belief that “poor” posture leads to pain is mostly based upon personal opinion, in that people theorize before they have any solid data, and they become subjectively and emotionally attached to the idea of “perfect” posture.
Trying to correct a person’s posture into an imaginary and made-up metric (norm) with no validity is a big waste of time. Especially when we even do not know what to correct the posture into! or if we, in fact, can correct the posture of another human being or that any specific posture is ideal or cause pain!”