Surely you should go by the rating, and your own individual child?
From the BBFC classification:
The ?12A? category exists only for cinema films. No one younger than 12 may see a ?12A? film in a cinema unless accompanied by an adult, and films classified ?12A? are not recommended for a child below 12. An adult may take a younger child if, in their judgement, the film is suitable for that particular child. In such circumstances, responsibility for allowing a child under 12 to view lies with the accompanying adult.
It's clearly saying it is the responsibility of the adult to judge whether their own individual child would be suitable to view it or not. It also clearly says that despite children under 12 being allowed if accompanied with an adult, it recommends no child under twelve should go in.
So you're child is 10 - of course you're not unreasonable not to take your child to view it.
To the person who complained - the option was there for you to decide not to go. There's been a few threads on this film, with parents of children of varying ages saying it was too much, or it was fine. So clearly it's down to your own judgement, hence the "A" part of the rating.