Besides the reef sharks that I have seen numerous times I have also dove in an aquarium with hammerheads and tiger sharks.
Since you mentioned this was in an aquarium, let me confirm; you did mean TIGER sharks, not SAND TIGER sharks? Big difference.
Adult great whites are very physically intimidating from what I see in photos & video. A huge animal, well-known as an apex predator, very powerful, with a huge mouth with multiple rows of large serrated teeth in jaws capable of immense crushing force, those strange black eyes that seem to have no iris, fast and stealthy in the water, and of course most of us at one time or another have seen simulated human attacks or recreations (Jaws movies, etc...) or watched footage of great whites in chummed waters, or breaching for sea lions off South Africa. A sea lion is a pretty good stand-in for a human, size-wise I'd think, and on t.v. they do show that seen from below there's a resemblance (especially if you're on a surf board).
Also consider that people don't like the thought of helplessness and panic while being attacked. If a shark did attack 'Jaws style,' swimming by biting hunks or biting you and shaking, imagine those rows of serrated teeth tearing into your skin, fat, muscle and organs, salt water rushing into the wounds, water getting in your mouth and throat, while you're screaming and thrashing in mind-blasting fear and unimaginable pain.
It's rare, but it does capture the imagination a bit, enough to make great whites the feature monster on lots of horror movies.
Remember; bathrooms kill far more humans than lightening bolts, but what scares people the most; thunderstorms or taking a shower?
Richard.
P.S.: I would love to cage dive with great whites, which would still be anxiety provoking, but deliberately getting into the water with a big one swimming around where I could see it and no cage? No. You can give a nice intellectual lecture on the irrationality of it, and I'm still not hopping in the water with a 16' great white and no cage. Diving off the coast of California knowing one might swim by without you knowing it would be one thing; deliberately getting in the water with one would be something else.