Eight words the Wiccan Rede fulfill,
An it harm none do what ye will.
The Wiccan Rede is possibly only a few decades old and may have been written by Aleister Crowley (not a Wiccan) or adapted from his works by Doreen Valiente (note the name, commonly thought of as the 'Mother of Wicca'; therefore she's the Pope figure that we don't have).
While this is the version recited publicly by Valiente in 1964, there is a longer poem of the same name. It was produced a decade later and published in Earth Magazine.
A minority of Wiccans don't accept the Wiccan Rede in their practice, but most do, as it encapsulates what it is we do, think and believe more than anything else.
What is the Rede saying? Superficially, it sounds like you can do what you want, as long as no-one's getting killed in the process, but try living by it for a while and you soon see that it's a little more complicated than that.
It helps if you can understand the words in it. 'An' isn't short for 'and', it's old English and means 'if'. In modern standard English then, the Rede says, 'do as you will IF it harms none'.
How do you interpret the 'harm'? Does it simply mean that you can't bludgeon to death the next person who upsets you? Or does it mean that you cannot harm in more subtle ways, e.g. insults or inconveniencing them? How do you interpret the 'none'? No-one except *insert prejudice or 'anyone who touches my kids'*? Or does it mean all human beings?
Furthermore, does it include all animals? How about fish? Insects? If you walk down the street and accidentally crush to death an ant, because it's dark and you didn't see it on the pavement, have you broken the Wiccan Rede?
Don't look to me for answers, because the other major thing about Wicca is that, as an active spiritual path, it is for you to decide. You are forging your own dialogue with the Gods, Goddesses and the natural world. You need to ask yourself how you are going to interpret 'harm none', which, in turn, could well be the most important question to meditate upon throughout your magical life.
One thing that I will add to your thoughts on the subject is that in not harming anything in the natural world, you have to include yourself. You are part of nature and you are your own closest access to the natural world. The Rede does not ask us to sacrifice ourselves unto death in order to fulfill the 'harm none', though anything which merely inconveniences us is probably on the line.
For example, I know of many people, who have become vegetarians because they determined that the 'harm none' didn't allow for them to kill another living thing, when they could survive without meat quite easily.
This is perfectly defensible, but what if, like my cousin, the vegetarian diet, no matter how carefully researched and balanced, ended up affecting your health? She's diabetic and anemic. In becoming a vegetarian, her body lost precisely the irreplaceable nutrients to keep her alive, thus she harmed herself. I personally would say that, in that instance, the first consideration, within the 'harm none', is not to kill herself.
Can you think of any other situation where not harming yourself might supersede the intent not to harm another?
Back to the Rede - 'An it harm none do what ye will'. We've looked at length about the first part of that, but what about the second? 'Do what ye will' doesn't say 'do what you want' or 'do what you fancy', it quite specifically says, 'will'.
There's a reason for this, which is in the triple meaning of the word 'will'. It can mean 'want' and it can mean 'stuff you want to happen after you're dead'. We're interested in the third meaning, which is summed up in the saying, 'where there's a will, there's a way'.
It's all about willing something to happen. As a Christian, Jew or Muslim, you might pray to deity to try and affect something out of your control in this world. You would be willing deity to intercede; speaking or thinking very, very hard to influence what happens next.
In Wiccan terms, you will be doing energy-work, which is also known as spellwork. You will be doing witchcraft.