Ive spent a good part of my life working in those sorts of environments, and all the while wearing a gun. If you think its dusty in an open room, try spending the day in concrete structures, like manholes, inlet boxes, etc, with a demo saw cutting holes for pipes that were missed or changed. Even wearing an N95 mask the whole time (you weren't breathing otherwise), you still had a nose full of crap at the end of the day.
Ive only more recently switched over to a red dot on my carry guns, and wasn't carrying one when I was doing that sort of thing, but knowing what the guns I was carrying looked like at the end of the day when I was, and from what Ive seen now, still occasionally doing similar stuff, Im not seeing it being an issue, as long as you stay on top of things with your daily maintenance, as you should be anyway. If you are carrying the gun IWB, with a garment with a fairly tight weave over it, you get very little crap on it. Carry it in something like a Smart Carry, and you wont see any. You still need to maintain your stuff, but its not at all bad if you pay attention.
One of my biggest concerns when I was considering switching over to the dots was whats being discussed here, crap on the screens. And all I asked that had been carrying with one for a while, said it hadn't been an issue. And I realize and took into account that most people don't live and work in those types of environments and knew the only way I was going to know for sure, was to just do it and see. So far, it hasn't been an issue, even on those "dirty" days. I verify things (screens are clear, dots are the right brightness, etc) twice a day, and hit the gun at night with an air can just before bed, when I adjust the dots brightness. I have yet to see the glass have enough of a build-up of anything on it that it wouldn't work. Generally, if there is anything, its a light bit of clothing lint/dust bunnies, which is gone with a quick "puff".
Maybe if you're someone who doesn't keep up on things, you may run into an issue, but I think if you use a little common sense and maintain things appropriately to your daily needs, its not likely going to be a problem.
As far as the video clip there at the end. Best be careful what you post there, you'll burst a lot of bubbles with stuff like that.
Things like multiple attackers in nice neighborhoods when and where you arent supposed to expect things like that to happen, doesn't fit what you're always told around here. There are rules, dont'cha know! And that kind of stuff isnt supposed to happen.