An it harm none, do as ye will

I suppose the alternative title for this entry would be "ignorance is bliss?" It's a question I've been pondering in many forms over the past few weeks, and one that I have not yet found an answer to. If you do something that has the potential to hurt someone else, but they never find out - is that ok?
My initial gut reaction is, or was, "No, no, no! You've done the thing and that is wrong in itself." but as I consider it more, I'm inclined to revise my opinion. In a simple sense, what you don't know, can't hurt you. Of course, if you then do come to know, retrospectively what was done in the past that you didn't know about has the power to hurt you, and also to damage previous memories and experiences. Wow - that was a sentence and a half. However, my point stands; finding out that things aren't as they initially seemed can make you question the intentions and motivations of people in past situations.
For example, I discovered in my mid teens that my dad was a smoker, had been for many years. My mother knew, but disapproved, so for this reason it was kept covered up. He smoked when away from home and none of the family could see him. When he was doing this, I suppose, he was causing no harm (to us at any rate, his body, another topic entirely and not one I intend to broach.) and it highlights my naivety that I just thought all cars naturally smelt like ashtrays. When I found out I was furious at the betrayal and hypocrisy, as I had had it very firmly drummed into me that I was never to smoke, and been berated by my mother for carrying a lighter (at the time, genuinely, I had never smoked! But I had a lot of friends that did, and a lighter is always a handy thing to have.)
It made me realise that as a young child when I had woken up in the car and seen my dad catch sight of me and throw his dog-end out of the window, that it wasn't, as my mother had convinced me, just a dream. I had in fact been deliberately manipulated into thinking my brain was playing tricks on me! But, when I didn't know, it didn't harm me.
Workplace bitching; we all know it goes on, but if I don't know the specifics for sure, I'm not bothered that my colleagues are bad-mouthing me; just so long as it doesn't get back to me. When it does, it upsets me and means I can't trust them because I know what is being said. Or might be said in future, or might have been said and I just don't know about it yet. Do I mind them saying it at all? I don't know. I can't change what they think, I disapprove of what they say, but I will defend to death their right to say it. So long as I don't have to listen.
So, can we live our lives like Thelma & Louise? Can we simply decide "let's not get caught," and go on with things regardless? What if our best laid plans fail and we do get caught in whatever act? "I never meant you to find out," is a somewhat cowardly defence.
In conclusion - I don't know. Is it the action itself that causes the harm, or the knowledge of it? Adam and Eve did nothing wrong by being naked, but when they knew they were naked, the trouble started.
Donald Rumsfeld was mocked for this quotation, but I think the guy had a point:
"Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns -- the ones we don't know we don't know."
Is a known unknown worse than a known known? Does that make an unknown unknown ok? Who knows.