I am not sure I completely understand your question but it is not sensible to go thorugh life completely ignoring or outright rulling out any possitive claims that we don’t have evidence for, especially when it comes to things still out of our reach. You are right that the positive claim is the one that requires proof; but we must also aknowledge our limitations. Consider a reverse of this:
1) Abiogenesis is a positive claim
2) We don’t have evidence ...