There's nothing irrational about fear of judgement. I do things that are completely legal that, if many other people knew I did them, would cause them to treat me differently, to my detriment.
You seem to be saying that I shouldn't hide them. My choice is to stop doing something I like doing, or accept that people will judge me and I will be treated a little worse. Why? Why should I have to do that? Why can't I keep going as I am? It makes me happier, it makes everyone else happier. What's so fucking wonderful about me being less happy?
People without secrets are perpetually putting on a show; removing privacy won't cause everyone to suddenly accept everyone's differences. You have some kind of utopian fantasy in which if everyone knows everything about everyone else, the world magically becomes a better place. It's not true. Tolerance has no limits? Have you met humans? How about that tribe where a boy becomes a man by being anally raped by other men? Or the neighbouring tribe where he becomes a man by orally servicing other men? There are cultures and societies in the world where anally raping children is simply not tolerated. How about gender selection? Killing a healthy child a few hours old because you wanted the other sex? The society I live in has a very low tolerance for drowning children in a bucket. Extreme examples, yes, but making it public won't suddenly make everyone tolerate it, and won't make everyone agree "oh, well they're different, it's okay for them to be like that".
We are different. Differences lead to disagreement and conflict. Privacy, amongst other things, gives everyone a means to shield their differences; be it something legal that society disapproves of, or something illegal that everyone does anyway, or something that's illegal in other cultures, or just odd. It's a necessary part of living in this world without either spending our time killing each other, or ending up a bland monoculture in which nobody ever steps outside the lines of society's accepted behaviour.