There's a gradual process to go from hypothesis to theory to fact, and to get there, you need several types of independent evidence. Correlational evidence is okay as one of those.
A correct statement is that correlation is not proof of causation (no matter how strong).
Types of evidence:
* Correlation
* Theoretical basis / strong hypothesis
* Extrapolation
* Interpolation
* Small-scale well-controlled experiments (lab setting)
* Large-scale less controlled experiments (real-world setting)
* Anecdotes
* ... and so on
You want several of those before you start to believe anything, and some are stronger than others. Correlation isn't fundamentally weaker than most of those, though; all of those carry their own methodological issues. The number of times you can have a large-scale perfectly-controlled preregistered randomized control trial with no confounding effects is exceptionally rare (some medical trials, and a few other settings).