Amaral's Book isn't clearly an opinion to me. In My Opinion.
The McCann's stance is either The Truth or A Lie. It is not an Opinion. In My Opinion. But there has never been any proof that it is A Lie. So please don't assume. Either The McCanns lied or they didn't. You appear to think that The McCanns Lied. I think that they didn't Lie. So these opinions lie only between thee and me. But you have no proof and I don't need any proof.
Well the Portuguese courts and the ECHR ruled that Amaral's book was an opinion, so what you think is irrelevant. It was also pointed out that the last word by the Portuguese authorities was that the crime wasn't known.
The situation in the UK is slightly different in that an ongoing investigation into stranger abduction exists. No-one knows why that is so, but it's not suceeded in finding a guilty party and neither has anyone else. The McCanns could ask Operation Grange to testify with their proof that it was stranger abduction, but I very much doubt they would do so. Even if they did, there's nothing to prevent people from disagreeing, especially in a book published in 2008.