Those aligned with the Dark Arts didn't generally care about what Muggles saw or not, and in Remus' opinion often thought too grandiose, too violent, too large to think about the littlest actions which could get under their guard. He wasn't blind to the fact that in turn, sometimes their side didn't think big enough.

"Know? Yes. We're all generally taught to do it, but practice? No. Most wizards have no need to practice silent casting and without practice, they'll fail in combat situations."