IMHO everything that we add to a freshwater system is at some level, stressful to the fish. Including salt, and including raising temp levels. Some species much more than others. I'm fine with people raising temps and adding salt, but not when meds are in the water. Cupramine works, Mardel Coppersafe works well too, both are very effective at eradicating ectoparasites without any additional help. I just think that when giving general advice, it's the safest way to go.
More dissolved things in the water and higher temperature results in less "space' for oxygen in the water. If I can help it, I generally don't raise the temperature when medicating.