I think the most controversial thing you actually said is "valid". That word is very ambiguous, and it's no surprise there's disagreement around it.
You can definitely make any interpretation you want. They will be valuable as long as you can take something from them, regardless of the author intent. As you have just shown, even authors might change or make additional interpretations as time passes. The world keeps changing, the contexts change, and we make new interpretations. That's pretty cool. But the other thing is whether they are true or not (whether they reflect something that the author really attempted to express). In this case, it's not strange to me that many authors want to explicitly say that they didn't attempt to hide some political meaning or similar behind their works. The problem is not that people reads into what they write, but that they attribute to them things they never meant. And that's an imposition on an author, which is not nice, and that's what a lot of people will discuss with you when you say that any interpretations are "valid".
If a politician tells you what he meant to say in a speech do you take it at face value? People lie to themselves and others all the time about what they have said and why they said it.
The text is the truth. What the author says about it is useful but not the end of the story.
You can definitely make any interpretation you want. They will be valuable as long as you can take something from them, regardless of the author intent. As you have just shown, even authors might change or make additional interpretations as time passes. The world keeps changing, the contexts change, and we make new interpretations. That's pretty cool. But the other thing is whether they are true or not (whether they reflect something that the author really attempted to express). In this case, it's not strange to me that many authors want to explicitly say that they didn't attempt to hide some political meaning or similar behind their works. The problem is not that people reads into what they write, but that they attribute to them things they never meant. And that's an imposition on an author, which is not nice, and that's what a lot of people will discuss with you when you say that any interpretations are "valid".