Personally, I see it as a huge house of cards. If hackers can get into otherwise very secure computers at the highest level government agencies, why would anyone expect they could not break into and steal from this system?
My personal thoughts are that “crooks” will break into the system, not in one big theft. but rather steal smaller but still very rewarding amounts on an ongoing basis so they are not noticed.... and probably already are!
I think this fear comes from a lack of understanding of "the system". In truth there is no central system. There is no server to hack.
I find it interesting (and you should too) that the computer scientists who know the most about "the system" of bitcoin are 1 - more likely to buy bitcoin and 2- less fearful of someone "hacking the system". It's just not possible.
It would be similar to saying you don't think email is a viable long term means of communication. YOU might get YOUR email hacked. Yahoo might get hacked and expose lots of people's email. But "email" itself is not going to crash or become unsustainable.