This was an isolated incident, the result of an appalling lack of judgment and sensitivity on the part of one officer, and has produced an unreserved and sincere apology from the Police, plus the payment of a substantial cash sum to the boy's school fund. What more do you want?
If you think that you can effectively protect the people of this country from terrorist activities without an occasional mistake being made you're living in cloud-cuckoo land. Spend a few moments thinking about what it must be like to be an officer in the Channel tunnel policing unit, or at an airport, or at any point of entry into the country. You would be acutely aware of the need for constant vigilance, and of the fact that, were you to make a mistake in another direction, and allow people in who subsequently committed an atrocity of some kind there would be no shortage of people - perhaps like you - who were only too eager to come down on you like a ton of bricks.
It's so often the case nowadays that the police are damned if they do, and damned if they don't. This error was made disgraceful by the way that the police handled it, not because they stopped a suspect. It's their job to stop people they suspect, and of course they'll get it wrong sometimes. So would I, and so would you.