OK I’ll bite.
The purpose of the ASIC system was to remove anyone with a criminal background from the front end of Aviation industry. The criminal background check does that. It also conveniently dovetails with CASA regulations which criminalise breaches of regulations. It thus helps CASA control industry employment or participation. This is also what was allegedly done to Glen Buckley although not through the ASIC denial route.
In this manner “undesirables” are prevented from employment in selected industries. The practice is creeping into use more generally in my opinion and it has some rather nasty human rights implications that will surface eventually. The practice does give the general public a warm feeling.
Preventing terrorism? How? Not possible.