It's clear whatever lead writer at Larian sees the relationship as at least always moderately abusive, or this would never have been changed to the default. They probably added this to clarify how the player is meant to interpret the romance, but it wasn't popular with the hardcore fans. Said fans will be against it even being optional, as it's a reminder of the canon reading as determined by Larian, which they disagree with. If it's on the table, it might still be true, you know? Best to banish it into the depths of the abyss. It's a non-negotiable.
If a player character can *emotionally* react in two ways to the same scene, after all, it's only logical that both reactions be somewhat "valid". If both are valid, both are a reasonable response. What would it say about the romance if fear is a reasonable response? That's it abusive. It's natural some people will be vehemently against the inclusion. Having it even be optional is indeed a direct violation of their headcanon. A win-win for everyone is not reasonably possible. Even if you hide the trigger behind a one time dialogue choice, some people will be angry. The knowledge that's it's a supported reading of the same romance they're playing is not something they're able to ignore.
We can only speculate why this change happened in the first place, because we've yet to hear an explanation. We don't know whether it was supposed to push the abuser narrative or they thought it was very kinky and Tav simply liked to roleplay being a helpless victim or they actually wanted to please people who like non-con since they already catered to discord shitposters with Halsin, and gave us squid tentacle action, etc. We can only tell how it affected us personally. Hardcore fans? How about all the people who never posted here and created accounts on this forum just to let Larian know how extremely hurt they were by this patch? What these fans you talk about want is for the narrative to be open to interpretation as before. Larian themselves said there is no canon story, only your story and you can do with the characters what you want.
There are several options to express fear of AA. I don't see how someone who is scared of him would continuously ask for a kiss and have the same panicked expression every single time. Their best chance is not agreeing to being turned or breaking up with him while they still have tadpoles in their heads.
