I think every group has it's extremeists, and IDA is no exception. There might even be a few among us
I try to use DS-friendly practices whenever practical in my lighting jobs, such as my cutoff driveway light, but would also gladly use a historical light within reason if I had one.
I think that the main source of light pollution isn't people's mercury vapor barn buckets, but most of it comes from street and commercial lot lighting. Banning MV barn buckets isn't going to make the orange glow over my home town go away. I believe some of that came from poorly planned lighting conversions.
In my home town, they would go through and replace a 400w mercury vapor light with a 400 watt high pressure sodium. True it maybe a full cutoff cobrahead, but all that extra light is now being focused down onto the ground (which is covered with snow part of the year) and getting reflected back up.
Here in Louisiana, much of the street lighting is from Mercury Vapor NEMA lights at 175 watts. They provide nice lighting levels without much sky glow. Where they have been replaced with HPS, they use a near equivalent 100 watt NEMA. Again, skyglow isn't much of an issue.