I've been in public restrooms from time to time throughout my life. My opinion has never changed regardless how clean some of them may be. I have always and will most likely always refuse to use the facilities that are open to the public in general.
This aversion of mine extends to private restrooms as well. Whether it's the bathrooms at work (when I worked) or at the homes of those I hold near and dear. I just can't ... not even for the smallest of tasks. I can't bring myself to do it. If I do, you can bet it was a SERIOUS emergency situation.
My mother used to refer to me as many things but one of them was, "camel bladder" ... And while I'm unsure about the true size of a camel's bladder I can only assume she meant that I was able to hold my urine, among other things, for long periods of time. I still do to this day. I realize it's not good for me, yes. But neither are the nasty organisms thriving in the public restrooms. I'll take my chances with a kidney infection or UTI before I use a public facility. Fortunate for me, I've only had a kidney infection/UTI two times in my life and it had nothing to do with not 'going' ...
Perhaps I don't take in much fluid ... this is the only thing I can attribute it to. I simply do not need to utilize the facilities (even at home) more than 4 times a day. When I was younger I went 2 maybe 3x's a day and that was it. I'm sure as I age, as has already been shown in the past few years, this will continue to increase. I will opt for 'Depends' when in public at that point!