History tells us there is no reason to think some things lie beyond scientific explanation; scientists have a good track record in transgressing boundaries. One of the few boundaries yet to be challenged is the strange nature of quantum mechanics – atoms existing in two places at once, for example. Richard Feynman said no one can understand how it can be like that. But it is likely we’ll eventually find a theory that lies beneath quantum theory, and that the root of such oddities will be exposed. It’s worth pointing out that “explain” and “prove” are two different things. Exactly how life on earth got started can’t be proved: the fossil record doesn’t contain the earliest chemical progenitors of life. Nor can we prove our hypothesis about how the universe began – all we can do is line up the evidence and decide whether we think it’s convincing (it is).
As for keeping things off-limits, where’s the fun? And there would be no point. If you want something explained, the best thing you can do is tell scientists they mustn’t look into it. There’s no harm in understanding; if need be, you can ignore the inconvenient truths. Neuroscience has made it clear that humans don’t have free will, but that’s not going to make us reform the justice system, any more than our understanding of relative harm is going to make a government reclassify alcohol as a class A drug.