Scientists of all kinds avoid any confusion over the conclusions of research by stating the conclusions carefully. You'll often hear the statement, "There is no evidence that [blank]," which basically means that if we start with the assumption [not blank], we don't have enough evidence to reject that assumption with any reasonable degree of certainty. That could be the case after hundreds of peer-reviewed studies have attempted to demonstrate [blank], or it may be that no one has even tried. Either way, "There is no evidence that [blank]" is not at all the same claim as "There is evidence that [not blank]" and should not be treated as such. Case in point: when my firstborn was an infant, I heard from more than one source that there is no evidence that allowing a baby to "cry it out" causes any lasting psychological damage, but I wasn't about to let my son cry for hours at a stretch.
I think it is common for null hypotheses to go unnoticed or unacknowledged. There's always some kind of default belief. Consider the vaccination scare, still active in some quarters. I don't think that childhood vaccinations cause autism, and that conclusion is predicated on the belief that we shouldn't think that vaccines cause autism unless we have some good reason to do so. One could take the opposite belief as the default, once the possibility of a connection is raised: that vaccinations do cause autism, or some other kind of harm, unless we have strong reason to believe otherwise. I'm not sure if that belief is thoroughly unreasonable, but it is certainly subject to criticism. Such as: given all of the potential causes and potential effects in the universe, any pair chosen at random are extremely unlikely to be related, and therefore the reasonable default belief is that there is no causal relationship between any pair of randomly chosen events. And why are we focusing on autism in particular? Why not other disorders or diseases, or even positive effects, for that matter? Why not take the default belief to be that childhood vaccines cause pattern baldness later in life? And so forth. Apart from the reasonableness of the null itself, adopting the wrong null is costly if there is insufficient evidence to reject the null. If you avoid vaccines because you believe they cause autism, you risk disease that vaccines can prevent (and we have very good evidence for that).
Back to Tim Minchin: it hardly makes sense not to believe anything without evidence. A more defensible statement is that one will not deviate from some kind of baseline beliefs without sufficient evidence. Then the origin of these baseline beliefs becomes the issue. These baseline beliefs are often unstated and may even be subconscious. I doubt that the anti-vaccination crowd is thinking things through in the way I describe above. Opposition to vaccinations may arise from a fundamental belief in the ability of the human body to heal itself under some kind of natural conditions, or from a distrust of the medical establishment's ability to improve health in a substantive way. I suspect that anyone considering the vaccination question has some kind of predisposition toward one side of the debate or the other, and that this predisposition often goes unarticulated.
I can imagine all kinds of baseline beliefs that fuel conflict over social and political issues. For example:
- People are basically good (or bad)
- Government agencies are generally corrupt (or trustworthy)
- Life on Earth is generally getting better (or worse)
Tim Minchin's disbelief in God is a matter of faith. Nothing wrong with that, and he can try to argue that this belief is somehow better or more reasonable than the opposite belief. But he can't claim that he is on the side of objective truth.