Basically it boiled down to this: I was suggesting that one reason some people might donate to more than one charity is that they're risk averse and want to make sure they're doing some good, instead of trying to help and unluckily choosing an unpredictably bad charity. It was admittedly a pretty pedantic point, but someone apparently didn't like it.

That seems to be something I would agree with, with an explicit acknowledgement that it relies on a combination of risk aversion and non-consequentialist values.