Your comment feels like gaslighting, considering you already know the answer to the question since OP is the one who suggested banning it.
There is really something weird with our virtual tools: we tolerate things that we would consider bonkers IRL. Like a newspaper shop asking for your phone number before you can read an article, or a library reporting the books you buy to the local candy shop.
A/B testing is one of those things: you have product you paid for, and the people who sold you the product change it without telling you, then revert abruptly the change, like it was a bad dream. But only sometimes, and not for your friends, who think you are crazy to believe it happened.
Anyway, there is an easy test to know if what you are doing is the right thing: ask the users if they want to opt-in. Most of them won't say yes, because, who would want that? Like tracking and advertising, only a tiny minority of users are actually ok with it if they have a choice. If you had a ublock origin for A/B testing, wouldn't you use it?
The only thing this test doesn't work with are duties and chores, like payment. But A/B testing is neither of those.
I think backend/performance-related testing, opt-in testing, and internal employee A/B rollouts are fine though.
An A/B test in such an instance is a HUGE diservice. I imagine there are others, but that that is what I can immediately relate to.
In such a case, I would feel like whomever implemented the A/B test directly caused needless pain and suffering: both of our frustrations and whatever inadequacies/helplessness my mother might feel.
So yes, I'm in the same boat: either make it opt-in, or make it illegal.
Nobody would think this is alright.
Besides, I'm advocating for _non explicit_ A/B testing. Let the people know you are fucking with them at least.