Being a Platonist and a frequentist aren't the same thing, but they correlate because they're both errors in thinking.
The objection to frequentism is that it builds the answer into the solution so the problem actually changes from the original real world problem. This is fine as long as you can test discrepancies between theory and practice, but that's not always going to possible.
I can afford cryonics, but I think I wouldn't want to vitrify children for the same reasons you are criticizing parents for having children. If it is ethical to bring children into the world only if I can care for them, protect them and provide for them, how could it be ethical to send a helpless, dependent child to an even more indeterminate future -- a future in which I have less means and knowledge to care for them than I do now?