The problem is folks, that many of these opinions start with "I don't believe in...:" All of these "controversial' concepts are not a religion, a political ideology or, a philosophical approach to life. Most of the stuff that folks around here get all riled up about are merely TOOLS at everyone's disposal to use or decline as they please.
It like my saying "I don't believe in HAMMERS"! Well, I don't believe a sledgehammer should be used for fine cabinetry, or a ball-peen hammer be used to extract nails, or a jackhammer to be used for dentistry! There a time, place and usage for every tool.
There is no law, ethic, moral covenant, or rule that says every time you pick up and camera and make a photograph it has to be pure and exactly as the eye sees the subject. If you want to work this way, that's alright and perhaps commendable but not everyone is of the same mind nor does everyone who does photography professionally have that luxury. Some folks like to experiment and try various methods and not every experiment will yield perfect results. As others here have alluded to, every method can be perfectly executed or poorly crafted and it is everything in between.
As for sky replacement- There are instances where improving the skyscape in a landscape, architectural or commercial image may serve as an improvement. Some of the software has pre-sets with a wide variety of clouds, sky, weather, night and day, stars, meteor showers, sunsets and moonrises, northern lights, and light-direction alternatives. It's up to the operator to find a compatible one with compatible actual lighting on the ground. Someof the software has a land-lighting option to alter the colour or effect on the ground so there is a unity of light as to quality and direction. There are also horrizion and feather edge adjustments. Using all of the theses controls effectively, and producing a more accurate and believable rendition requires skill and knowledge of light dynamics and aesthetics you are gonna end up with a "patch job". If you are gonna mess with Mother Nature, you better learn her ways or folks in the know are gonna scrutinize and criticize your work- OR NOT! You can ignore them and just have fun or consider their suggestions and improve your technique. But it ain't religion, politics or life and death!
It's the same in portrait lighting- folks defy nature every day. They use 2 kicker lights from opposite directions, light a portrait with 2 equidistant 45-degree lights- that would be realistic if there were 2 suns in the sky. They "clamshell" light a subject- that would be accurate of one of the 2- suns were coming up out of the ground. Yet, these have become acceptable stylizations.
Many of the protracted and repetitive arguments are GEAR-driven- filters, software platforms, lens shades, flash. and all the other photographic headwear. There is little discussion of light dynamics that apply across the board to artificial and natural lighting aesthetics that have to do with the sky, the clouds, the weather the time of day, the hour, the atmosphere, reflectivity, the direction from where the light is coming from, and the way it strikes any given subject.
For years the folks who design and manufacture lighting equipment have been trying to figure out how to stimulate the light that comes down from the sky. Think about the names- Sunpack, Megalume, Skylighter. Starlighter, Hazylight, Ultrablitz, White Lightning- I'm sure there are more. All you have in many cases is a sophisticated ligh bulb in some kind of housing and YOU have to figure out how to use it in order to achieve the results you want.
My favourite is Photogenic's names for its flash gear, Flashmaster and Studiomaster. I once joked with the sales rep from that company at a convention. I said that this "Master" equipment is extremely bare-bones- no automation, just basically a power supply and a flash tube in a plain parabolic reflector, so if I buy this stuff, will I become "Master". He said no, it's basic TOOLS, you need to be a "Master" to maximize the results you get out of it.