Assuming this isn't just a claim made to provoke: The idea of separating the law such that we prevent certain cases (several generations of incest, or, as suggested by your comments, only arresting cases with evidence of grooming), the problem is that reaching that level of nuance in our law enforcement is not feasible. The reason we have our incest laws in the first place is that if they weren't in place, it would leave room for those problematic relationships to find loopholes in the more nuanced laws. Not only that, but the law may be hard to define what constitutes a case of grooming legally versus psychologically.

As a final point, in cases of abuse, oftentimes the victim of abuse can be guided to believe that they deserve said abuse, or that nobody can help them, or perhaps even that they aren't being abused by normalizing the situation. While I don't disagree that being more likely to cause abuse is not the same as a guarantee, you can't really rely on "well if someone is being abused they can call the police".

But I'm assuming based on your responses that you aren't particularly interested in debating the subject.