Well then communicate your wishes to whoever develops the browser you use. Websites are just complying with what your browser is telling them you prefer. It's your browser that's not giving you the option to change what it tells websites to suit your preference.
So, we still have the same problem. Web-sites think—despite there is being no way to tell that a user doesn't want dark web-site theme, just uses dark UI—that they should definitely unarguably force on a user dark theme. If it's obvious that there is no way to tell exactly what a user wants, but only tell what browser UI a user uses, maybe it'd be more reasonable not to force dark defaults just because the browser has dark UI.
All you have to do is look at all of the replies to your post here on HN to understand that the majority of users who have their OS set to dark mode actually do prefer websites to display in dark mode as well. This is probably why browsers don't (currently) offer an override option.
You are free to have an opinion, but I'm so confused as to why you're not understanding that it's a minority opinion and that the way things work currently actually do make sense.
Those who write angry responses with an opposite opinion are not a majority. That's could be an example of a vocal minority. If some people are loud in their disagreement doesn't mean they are a majority. Those who agree often don't bother to write. That's an understandable mistake that often leads to wrong conclusions. Just judging by comments here is not very useful.
“Doctor doctor, it hurts when I hit myself with a hammer”
“Why don’t you stop hitting yourself with a hammer?”
“Hammers exist to be massage tools. It’s the manufaturer’s fault, they should make them softer. I know lots of people are disagreeing with me, but they’re just a vocal minority, the silent majority want soft hammers!”
Your opinion on how websites should respond to user preferences is a bit off the wall, to be frank. There aren't many (any?) angry responses here, but there are a lot of responses trying to explain how the current way it works makes sense despite your own opinion to the contrary.
It seems to me like you're just not handling disagreement very well, and that might be something to work on for the future. Especially if you're going to post your opinion publicly.
