why would the post use the tone "I don’t want" in "I don’t want my users knowing that I’m handing them an interface."
This is a cite from the "Clean Code" book by Robert Martin, a.k.a "Uncle Bob". And though Robert Martin is surely a respectable and experienced software engineer, he is often critized for his tone. Many people think it is too "schoolmasterly", especially in the mentioned book.
In the sentence you asked about, I guess Bob Martin intentionally"I don't want my users knowing ..." puts his ownBob Martin's thought process way of thinking into the center of histhe explanation, not the users' point of view. He could have also written "I don't want my users' need to know ...""I don't want my software to be designed in a way that my users need to know ...", but that does not sound sowould have been far longer, less striking and less memorable.
My recommendation: just read everything what Robert Martin wrote with a grain of salt, don't take him too literally and don't take his. His statements and writings asare recommendations, not dogmas. Then you can learn a lot from them.