I understand what you're saying, that in a legalistic way it qualifies as dubcon - but the way it's written, it really feels like noncon, and I understand why everyone's reacting that way. I have different reactions between reading dubcon and noncon, and maybe our definitions vary (there's certainly a thin, daresay dubious line), but I definitely got the "ooer noncon" reaction to this.
I think what makes it so is one, what you correctly said that Sam does not even have the full power of consent here - just because he doesn't tell Dean to stop doesn't mean it's not noncon. Two, what I really found on the verge of squicky and darker than I prefer is Dean's thoughts and reasoning. The way he ignores the little ways Sam is trying to stop him, he reasons that this is okay and he can do all these things, and he's really not overly concerned with making sure it's okay with Sam. That's what makes this story and version of Dean an evil AU, since the Dean I know would never do anything without making sure it is absolutely 100% okay with Sammy, and he might die of guilt and horror if he ever thought he molested him. I don't mind him not freaking out about the incest factor, but particularly when Sam's still so young, I think Dean would be very concerned about "messing him up" some way. Also, your lines about how old Sam's eyes look, staring past Dean, are super-creepy and definitely tell readers Sam is not into this, and that is squicky. Especially because Dean isn't recognizing that.
Hopefully this is illuminative! You're still right this is technically dubcon, but you might want to make a note about how it may feel like noncon to readers, since a lot have said so.
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I think what makes it so is one, what you correctly said that Sam does not even have the full power of consent here - just because he doesn't tell Dean to stop doesn't mean it's not noncon. Two, what I really found on the verge of squicky and darker than I prefer is Dean's thoughts and reasoning. The way he ignores the little ways Sam is trying to stop him, he reasons that this is okay and he can do all these things, and he's really not overly concerned with making sure it's okay with Sam. That's what makes this story and version of Dean an evil AU, since the Dean I know would never do anything without making sure it is absolutely 100% okay with Sammy, and he might die of guilt and horror if he ever thought he molested him. I don't mind him not freaking out about the incest factor, but particularly when Sam's still so young, I think Dean would be very concerned about "messing him up" some way. Also, your lines about how old Sam's eyes look, staring past Dean, are super-creepy and definitely tell readers Sam is not into this, and that is squicky. Especially because Dean isn't recognizing that.
Hopefully this is illuminative! You're still right this is technically dubcon, but you might want to make a note about how it may feel like noncon to readers, since a lot have said so.