I'd think the conclusion you should draw is not that "even the famous experiments were not valid, so nothing in psychology is" but rather "the validity of an experiment does not correlate with how famous it is".
A direct conclusion. The insight I'll draw from that is that academia gives voice to the results the current zeitgeist finds interesting and believable without properly verifying the evidence.
Famous experiments are not chosen by academia. They are chosen by non academics. What you usually find is academics being much more reserved and more critical of these then journalists, bloggers or random commenters on HN.
I guess my point is that I don't need to think for long before I find an example justifying why physics is a serious field.
What would be the equivalent of Newton's laws in psychology? Does such a thing exist? Or does the whole field just prove how complicated human beings are by being incapable of proving anything else (which in itself would be an interesting result, don't get me wrong)?
Physics is an exact, quantitative, natural science. Psychology is neither exact, quantitative (usually), nor a natural science. They are not comparable. But like many other fields of study that are not hard sciences, psychology can still be useful and valuable. (Note the "can". Given the replication crisis, how much of psychology actually is I cannot say.)
But do we have an example of something that is provably valuable? I am genuinely interested: after reading this article, I realised that there is nothing I can attribute to psychology off the top of my head.
See also the replication crisis.