I may be putting words into the parent's mouth here, but I think the argument is just analogical. That there are emergent effects to physical processes that are difficult/nearly impossible to predict from basic physical law. And therefore we should withhold judgement about the difficulty of life forming, given that we so far have a limited understanding of the relevant physics.
Nah I mean it pretty literally. You are very right that the necessary physics isn't really there, this is a really difficult thing to state rigorously.
However I would argue that the underlying reasoning emerges out of fairly fundamental physics.. and that while difficult to state rigorously the core idea is kindof... obvious... to anyone with a strong physics background...
