Personally, I think that you are overdramatising and scaremongering (and though I am not Greek, I find your qualifications insulting). I have been to Athens multiple times in the recent years (and then more to the islands) and have seen / experienced nothing of what you are describing. This is a phenomenon attributable to all congregated places (especially ones popular among tourists) and one needs to exercise reasonable caution in principle (the heck, it happens even here in Vienna around Stephansdom ...).

In all honesty, in comparison, I actually find e.g. Brussels to be much worse in this respect and I felt much unsafer there as compared to any of my visits to Athens.

As another point of reference, I just returned from a short stay in Lisbon - one could clearly see those subjects, who truly stand out if one is careful, looking for victims around the popular tourist places. Even worse, there is no other big city that I have been to, where I was being approached every five minutes by random people on the street offering me to buy drugs, and then being visibly irritated when I declined (and the police just around the corner doing nothing about it).

Strangely enough, the only place I visited and got a valuable (my iPhone) stolen was Dubai ...