Is Causation a Purely Philosophical Question?

Here's an argument in favor of such a view (using largely Humean premises):

1. All beliefs are justified either a priori or a posteriori.
2. We have a justified belief in causation.
3. No beliefs about causation are justified a posteriori.
4. Therefore, all beliefs about causation are justified a priori.
5. Whatever is justified only a priori can never be confirmed by experimental evidence.
6. Therefore, beliefs about causation can never be confirmed by experimental evidence.
7. Whatever cannot be confirmed by experimental evidence is not an empirical hypothesis.
8. Therefore, hypotheses about causation are not empirical hypotheses.
9. All justified hypotheses are either empirical, logical, or metaphysical.
10. Causation is a justified hypothesis.
11. Causation is not justified empirically or logically.
12. Therefore, causation is justified metaphysically.