I'm not against this on principle (I'm a SCH myself), but here's the thing: first, Shadow Flare honestly does very little damage. Second, people are wrong when they call the wall a DPS check: pretty much any party can clear it as long as they handle the mechanics right.

So helping people deal with the mechanics should be your first priority. Sure if they did things right Shadow Flare wouldn't hinder them, but your teammates are who they are (especially in PU groups) and you won't change them by being frustrated. Just make their lives easier.