Before I got involved in HE, I would have agreed that it was a very small thing to ask HErs to let their children have a face-to-face meeting with an LA representative in the interests of finding the "wolves". A minor irritiation and inconvenience, which would help to protect vulnerable children - no problem.
But now that I know far more about it, I see the problem quite clearly.
In order to get the power to do this "small thing", a very big principle would have been established in law - that the decision to deregister a child from school in order to HE is automatically a basis for starting child welfare procedures.
Once that link is a legally established one, it opens the door to far more intrusion by LAs in how families live their lives.
At the moment, some LAs misuse the powers they have, and claim to have additional powers, in order to harass and intimidate innocent HE parents. Those parents who know the law can protect themselves from this interference. These LAs do this because they do not believe that parents should have the right to educate their children outside of school, or that they ought to be forced to follow the NC or take standard tests, or ought to be regularly inspected. All this despite the fact that it is perfectly legal in this country to opt out of the school system and accept responsibility for your own childrens education without using schools.
If those LAs had the right to invoke "child welfare" against HE families when there was no suspicion of anything apart from the HE itself, they would make use of it to further interfere in family life, and use it as a threat to ensure co-operation. They would also very soon start trying to get extra powers and control.
I'm a decent law-abiding citizen, as concerned about child welfare as anyone, and also about issues like terrorism. But anyone who has seen the way in which powers of surveillance gained under anti-terrorism legislation have been misused (eg to watch families who might have fraudulently applied for schools) can hardly doubt that the government (central and local) will not hesitate to make full use of any powers they have, regardless of whether that was the basis on which they got those powers.
If we allow this to happen, within a few years it will no longer be able to opt out of the school system to educate your children in the way you believe to be suitable for them. You may not think that matters, you may think schools are fine. But they are not fine for all children all of the time, and those children need an alternative.