The only time "report crimes" should be off, is when you specifically do not require security assistance for any form of protection. For example, smuggling runs and engaging in PVP.
If you are trading, for any reason outside of "illicit" then always enable report crimes; this will cause any security forces to scramble (although outside of station NFZ the value of this is highly debatable). However, the AI is still and cannot make 'value' judgements like humans. We instinctively know what the triggers are for many events; it's very hard to make an AI have any kind of instincts; classic example is being engaged by powerplay NPCs (who are enemy, but not wanted) gaining a bounty for dispatching one, and the cops roll in, only to attack you as the priority.
Open isn't the issue; the way AI react to crime, and the punishment/ retribution system isn't strong. It's actually very weak given the extremely high burst damage that is now available to a number of combat ships, which is only going to increase with new class 3/4 weapons.
It's really about time the entire crime system was reviewed; if you are in high-sec then the entire system should be crawling with itchy-trigger constables, that react rapidly to crime and swarm in large numbers. If you are in anarchy? then all bets are off. As it should be.