Why do I have permission to edit other members' questions?

I've been curious about the text link "Edit question", which shows up when reading a question/message. I assumed it would be a way to edit my own questions, and that it would produce an error if I clicked it in someone else's question. But when I clicked, it did open their question, and appeared that I could have edited if I wanted to. Maybe the error would come when I tried to save/submit the edit, but I'm hesitant to actually try it, because if it really does allow me to edit, I'm guessing there will be some indication that I edited it.

Anyway, my question is, why are questions/messages apparently editable by anyone? What purpose does it serve? Shouldn't the ability to edit anyone's message require some kind of advanced permission?

Thank you very much :-)