well ok, but while we are on the subject, we have no proof of any causation anywhere in the universe, all we have is the correlation that we've never seen (for example) gravity repel, only attract.
Not really true. If two things are strictly correlative, that means there is an additional factor causing both.
If you eliminate all reasonable additional factors (by controlling variables), you can demonstrate causation. Arguing that there can be unknowable external factors behind everything is not very scientific.
Identifying causal relationships involving humans is difficult due to the excessively multivariate nature of all our interactions, and by extension how difficult it is to "control" humans (as opposed to water, or a wheel). That does not mean it is impossible to ever demonstrate causation.
Leibniz denies the existence of causation in his Monadology[1]. In short, everything acts solely according to its own nature without any interaction with anything else, but in a harmonious way that creates the illusion of causation. That strikes me as a bit far fetched, but it does show that accepting the existence of causation is a metaphysical choice and not necessary.
> Leibniz denies the existence of causation in his Monadology
This sentence is incoherent unless one assumes the denial of causation is bunk, since it makes no sense to attribute either Monadology in general or the specific claims from it being discussed to Leibniz unless he caused the existence of the work, which clearly he cannot have if there is no causation.
