This has me thinking there should be a show on "If you are doing this you might be annoying others at WDW".
I have the start of a list to start adding to and going through:
- Cell phones for any reason on in dark experiences (TIL)
- Rude to CMs or Guests
- Not knowing your order before getting to the checkout at counter service
- Spreading out on seats leaving a "open seat" between your group members
- Not going to the end of the row
- Talking of any sort during a show (including whispering)
- Rejoining your group in line
- Saving spots around quick service prior to getting your food ordered
- Not merging every other person/group
- Reserving multiple ADRs for the same day but cancelling all but 1 right before the cancellation window
Yep, this is a pretty good starting list. These are all pretty standard rules that should be followed. (I would think that "Rude to" anyone would be considered at a minimum "annoying" in any context, not just at Disney, of course.) I've seen plenty of articles and threads on annoying behaviors at Disney, so they're out there if you want to look for more. (And, yes, talking in shows absolutely includes whispering - as close as people are, any sound is going to be audible, and just the sound of whispering is distracting for many, even if they can't make out the actual words being said.)
I recently saw someone give a description of unethical behavior as something that, if *everyone* did it, it would cause problems. So, for example, let's say on Halloween, if one person just dropped their candy wrapper where ever they opened it, it wouldn't be that big of a deal, most people wouldn't even notice a single candy wrapper on the sidewalk - but if *everyone* who ate a candy wrapper dropped them at random, the sidewalks would be covered in trash and it would cause a huge mess and everyone would be grossed out. So, then, to be a considerate member of society, you need to refrain from dropping your candy wrapper out in the open, not because that one wrapper would cause a problem on its own, but because you are part of a community that is all mutually agreeing to keep trash in trash bins in order to function.
The same thing is true here. Maybe in your case, for a couple seconds, you don't think your light is adding enough to the overall light in the area to cause enough of a difference - but if every single person on the ride had their phone out and casting light, then the whole place would be lit up and all the carefully designed lighting elements of the ride would be overcome by phone lights and none of the ride would appear as intended for anyone on the ride. The vehemence of the replies here is not because of your one exact situation - it's because the "community" of people riding Haunted Mansion have an unspoken agreement that since everyone can't have lights on without ruining the experience, then no one can have a light on at any point. Sure, one person might not technically make a difference, but who decides that you get to be that *one*?
The same rule works for everything else on your list - if *everyone* booked two ADRs for their own convenience, and then cancelled, then only half as many people would be able to book restaurant seating, leaving a ton of people unable to plan their day. If *everyone* from the left side of the line refused to take turns merging and just plowed through, no one from the right side would ever be able to go. So anyone choosing to disregard those guidelines is inherently deciding that they are more important than everyone else around them, because the others have to follow the rules in order for things to keep functioning, but the rule breakers have decided that doesn't apply to them.
Another reason for the extreme response is because so many of us have experienced people who weren't even trying to hide their light - people who had their phone on in the pre-show when it's supposed to be pitch-black, or people whose whispers carried much further than they expected. Those people didn't seem to think their actions were having an impact on those around them, but they were wrong - they were very distracting to us. So we already know that other peoples' perception of their impact on the surroundings doesn't always align with how others perceive it. No matter how certain you are that your light doesn't go beyond your buggy, you can only see it from your own perspective - you can't guarantee that no one else is affected by it.
Speaking personally, I am very sensitive to bright lights or "blue" lights when my eyes are adjusted for darkness as an after effect of my Lasik surgery. The blue light created by a phone is far more noticeable and distracting to than a "yellow" light (like the lamps in HM), even if they're technically the same intensity. Even a little bit of light from a phone can cause a "glow" that could be visible around your doom buggy if you're next to me, or the car might turn a little faster than you expect and I see your phone light beside me as we turn, taking my thoughts away from the ride and onto you. It's just not fair to others on the ride who want to be immersed in the experience as it's designed.