Pretty much a case of hammer, meet nail. 
Even the small fraction of the available literature I have in my collection, contains documentation of enough robust experiments to make life difficult for any honest objections to the postulates of prebiotic chemistry.
And, indeed, the subsurface oceans of both Europa and Enceladus are considered to be viable candidates for indigenous life of some sort, even if it’s only single celled life forms, because the extant conditions in those oceans are not that far removed from prebiotic Earth conditions.
There is one big exception to this, of course, and that centres upon the fact that those subsurface oceans are shut off from light, by tens of kilometres of overlaid ice. Which immediately rules out photosynthesising organisms. But there are alternative energy sources to call upon, if the deep geophysics of those bodies produce their own version of hydrothermal vents.
Discovery of actual indigenous life in those subsurface oceans would, of course, give us other models to investigate. But for me, discovery of something akin to an RNA world would be even better, for reasons I’ve already provided.