I have been on scuba hundreds of times with sharks, as well as swimming in the ocean or snorkeling with them around.
Mostly, they are just like any other fish: minding their own business, looking for food. If something they don't care for (like humans) comes too close to them, they move away.
Being around them when blood is in the water is not a big deal. In Honduras, I participated in a scuba-based shark feeding. The outfitter took a five gallon bucket of fish parts to the bottom of the Gulf of Mexico in about 40 or 50 feet of water while 12 or so divers watched from 15 or 20 feet away. As soon as the sealed bucket was opened, a lot of reef sharks swam in for a nibble of the fish. One shark bumped my arm in the frenzy, but only because two other sharks unexpectedly pushed him (or her?) out of the way. We were advised to keep arms and fingers close to our bodies to minimize the possibility of them being mistaken for a dead fish part. It had been a long time since there was an incident, even though they do this one or two times per day—for many years.
The most unexpected encounter I had was entering a shipwreck, which was mostly a hull, in the Florida Keys and not completely submerged, so the sun caused the water inside to be very warm, like 95°F/35°C which apparently about 500 nurse sharks were attracted to. As soon as I went in, they all decided they wanted out. It seemed they were rushing me, but in fact they were trying to go around me. Once I lay flat outside the opening, they quickly all vanished. Their lack of displacement induced a brief current which washed me into the wreck. This was about five feet of water.
Near Darwin Island, in the Galapagos is well-named Shark Alley. Every time of the dozen or so times I have been there I see anywhere from 1200 to 3000 sharks hanging out a foot or two above the white sandy bottom at about 90 or 100 feet deep in usually chilly water. I think these were six gill, mostly in the six to eight foot long range. They didn't move when I swam to them and photographed with a flash camera or shot video, at least until I got very close, like four feet away. Then they would move away a tiny bit.
The most exciting encounter I had was meeting a white tip reef shark off Vancouver Island (Barkley Sound) in low visibility water about 70 feet deep. He became boxed in a depression in rock reef, and I blocked off his exit when he first saw me. He swam vigorously one direction, stopped short of one rock, then went the other way. He was moving so fast, I popped up five or eight feet with excitement, and then he swam underneath and to open water.
If your source of information about shark behavior is the mass media, you have been seriously miseducated. Of the 300 known species of sharks, only four have been known to attack humans, and most of those which were not provoked are thought to be cases of mistaken identity. That is, humans were acting like dying prey in murky conditions.
thousands of scuba dives
thousands of hours swimming and snorkeling in oceans