Stopping knife crime

In yesterday's Metro (free London newspaper) there was an article about the reducing number of young people being prosecuted for being drunk and disorderly and the plans to introduce "knife arches" in schools. Frances Lawrence (the widow of murdered headmaster Philip Lawrence) is reported to have said that the machines which scan pupils for metal objects would cause distress and fail to address the issue of knife crime outside of schools. "I think this is the criminalisation of all young people...".

I am sorry but how does having to walk through a security scanner checking for knives and other metal objects criminalise all young people. Do the scanners at airports criminalise all passengers?