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I don't have time today to look into it, but I will this next week. I hope it is not the future of gtk2 apps to require an icon theme installed to function. But as it will be awkward to have an extension impose a .gtkrc-2.0 in the middle of desktop use, so I will look for a light default theme that can be a dependency of gtk2 and also copy a .gtkrc-2.0 to the home directory if it does not exist.
I believe hicolor-icon-theme is what apps like these should depend on, because it's small and considered "default". Apps should try to use it if no icon theme is specified.
An icon theme, unless required by an app, should be the choice of the user.