I don't want AI in my browser even if I can turn it off for the same reason I don't want my refrigerator door booby-trapped with an explosive even if I can turn it off.
Bugs happen. Configuration changes happen. User error happens. Software is complex, and I shouldn't need an intimate knowledge of every goddamn app I run to be sure it's not siphoning all my data off to god-knows-where. I use hundreds of programs on a daily basis. It is completely untenable to carefully configure every single one, stay abreast of constant updates and changes, and spend 76 full working days reading every TOS I am subject to. And of course, all their policies and defaults are subject to change without notice, so nothing I learn today will necessarily apply tomorrow anyway.
I want to be confident that my web browser is not — either by design, due to a misconfiguration, or due to a bug — sending my data to OpenAI. I do not want a booby-trapped browser, even if I can turn off the booby-traps. I do not want my fridge to explode, so I don't buy fridges with built-in explosives. Seems pretty simple to me.
I also want to be confident in the same for others. If I deploy a browser to 100 employees' machines, or even just my mom's, a little opt-out checkbox under Settings will not give me any peace of mind.
If Civilization II taught me one thing, it's that ongoing payments are an absolute scam... Unless you're planning to declare war anyway.