Anjaq : The mountains I hike tend to have a lot of poison ivy.

And I'm not very good at recognizing it... (I'm not sure if you have poison ivy in your area, but that is NOT something you want near the tender bits. It gets everywhere once you touch it, too, so to be perfectly honest I'm never 100% sure I don't have some on my hands/clothes while I'm out there.) Also, my impression is that one needs a bit less toilet paper with one of those doohickeys, at least, but either way, I'm more comfortable burying something biodegradable than finding out what happens when I grab/touch something I shouldn't.
I wouldn't risk standing to pee in a women's bathroom out of paranoia about the other *people* in there, so that's moot for me, but I'm sure you're right about the sanitary products bin.