1 - I don't see sunscreen impacting the reef as much as you might think. Think of all the other pollutants in the water, and then think how few people are ever around a reef at all. It would be so diluted it would have little, if any, impact IMO. This should come down to just personal conservation of anything though. If you feel strongly about it, wear reef safe sunscreen and advise others to do it as well without offensive about it. It just takes one person's opinion to change someone else's mind.
2 - It depends on the swim through. If they are highly decorated or have delicate corals growing on them, stay away if you aren't able to get close enough to them without damaging them. As for the air bubbles, if they get trapped in a coral, they can cause local die-off in that particular spot. But also think of the odds of this happening. Think of the strong ocean currents, waves, etc constantly moving the water, fish, critters and coral around. It's highly unlikely a bubble will be trapped in a coral unless someone is just sitting under a swimthrough venting off tons of gas.
3 - Again, how many times do the fish get harassed over their life span? Chances are a fish that got a flash in the face or a flashlight in their face is never going to be seen again by the time the next group of divers come by. Sure there are resident fish in some nooks and crannies, but if it bothers them, they will move. That's how fish are. They don't stick around if they are being bothered or threatened. The only argument against this is on night dives, we see when we're out lobstering at night, a lot of fish are either stunned at the bright light, but quickly adjust and swim away or they are attracted to the light and want to see what the light is (some follow us, its quite amusing). Some fish, while they may appear stunned, are actually sleeping and won't notice anyway. I can also observe this in my own reef aquarium as well when looking for stuff in the rocks with bright lights.
I wouldn't say they are in jeopardy as it's probably does the same as it does if your buddy shines their light in your eyes at night..its blinding for a moment (remember, you're also prey in the ocean) but your eyes quickly adjust and you're fine. I wouldn't suggest just burning a hole in the poor fish or critter with your light, but general swimming around looking at stuff isn't really impacting them as much as you might think.
5 - As for the gopro comment, or any other photograph device... if the fish don't like it, they will swim away until you leave. They aren't going to remember you being there in a minute anyway and will go back to their task of doing whatever they were doing. And as stated above, chances are that one fish will probably never be seen again by divers to be "constantly harassed" (unless its a big resident grouper or eel or something that stays in one place..and they aren't the least bit worried about you).
If you want to learn about reef conservation, join a local reef group for your area, or start a reef aquarium and learn that way (most cities have local reef/aquarium groups as well). It's an incredible thing to watch and care for a living reef and learn how it functions in a smaller environment. You would be surprised how hardy they are for some things and how delicate they are for others.
The best way we can protect our reefs is to make people aware of damage to it...via anchors, fishing, boating, and the BIGGEST thing...keeping divers off the bottom! One "oops" just killed 100's of organisms that took many years to grow
Hope that helps some.
