Also, the null hypothesis is just a starting point from which you gather and analyse the data that may disprove it. There's no reason that 'X has no effect on Y

Also, the null hypothesis is just a starting point from which you gather and analyse the data that may disprove it. There's no reason that 'X has no effect on Y' should have a privileged position in messy real-world epistemology; we don't assume that nothing causes anything in the absence of conclusive proof, we keep an open mind and make our best guess based on whatever information we have.