Figshare has a FAQ that covers this, sort of. Whether the Panton Principles were formulated using the same reasoning I do not know, but I have heard the Figshare reasoning on several occasions. Dryad has a stronger and more lengthy explanation (click on "Why does Dryad use Creative Commons Zero" in their FAQs).
The fear is that since some data cannot be copyrighted, if you use something other than CC0, people may not realize that some data can be used without attribution (as it is not subject to copyright). This reduces use of the data, which is contrary to the goals of openness.
The claim has also been made that it might make various sorts of data aggregation difficult. Dryad, for instance, imagines that you can competently aggregate data from 50,000 sources and asks you to envision lawsuits from not attributing the sources.
Both of these strike me as tantamount to saying, "We are are bad programmers, and careless scientists."
Scientifically, you want to know where your data comes from so you can fix it if the upstream source fixes it. You don't want messy aggregate data sources with no idea where it came from. Yes, you have to be a good enough programmer to keep the tiny bit of metadata about where it came from (and can be used for attribution) associated with the data itself. For instance, if you can grab data from 50,000 sources and can't even manage to say who it is from, what confidence should we have in the quality of your work, analysis, conclusions, etc.? Having licenses enforce this kind of basic good practice seems like an advantage, not a detriment, to me.
That doesn't mean that every license is appropriate for data. Viral non-commercial licenses really limit how data can be used, as once they get mixed in to a data set, companies basically have to stop touching the data. Contrary to the ideal of sharing, this actually poisons sharing by legally enforcing a forbidden class. But the idea that CC0 is the only thing that's appropriate for data is not well-founded, even if it is a common view. CC-BY is really not problematic; the requirements are minimal. (In fact, Figshare sensibly allows CC-BY for figures and so on; last I checked, Dryad insists on CC0 for everything. And both say you should provide attribution anyway as good custom.)
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