Sexual Abuse Support Group

I think that for a situation to be abusive the best determining factor is if one of the people were taken advantage of (less aware, drunk, emotionally unstable, etc.)

Many would consider it illegal or immoral, regardless of the question of abuse. Legally none of the above are abuse, to my best knowledge.

Does it become "more abusive" if one family member was more "aware" than the other, regardless of age?

I do think it is possible for situations involving 2 consenting adults to be abusive, such as prostitution. I am also outside the normal viewpoints because I consider consentual domination to also be abusive - I don't care if a person "agreed" to being dominated. However, there are many who would argue that I am wrong in both cases and at that point it becomes an arguement on morals and the right for a person to choose for themselves (hey, suicide is illegal right? why not acts that strongly devalue a person?)

I agree there are instances where incest isnt abuse but could be consentual or experimentation.
For it to be abuse I think there needs to be force or manipulation or a big age gap where one person is at a mature age and should know better. The abuser may use threats or bribes to have their way. I think with siblings, one may only be 2-3 years older but they are usually taught by the parents to look after the younger one. The parents give them authority and the younger one is told to respect and listen to the older one. So it wouldnt take alot for an older sibling to coerce a younger one. I have a sibling only 2 years older but I looked up to her and she had authority over me. I trusted her judgement. If she had initiated sexual stuff with me and without much pressure I had gone along with it then I would consider this as possibly abusive.
This can be a bit of a grey area and not clear cut like an adult abusing a child.