I think alignment should at least be present for enemy creatures purely cause I think there are a few things in 5e that actually do care about alignment and it does act as good shorthand for less complex creatures where the goal is not to get into the complexities and grayness. Like a random Demon from the Abyss should likely be marked as Chaotic Evil, while if somehow we got a demon as a companion it should have no marked alignment because the situation would be more complex.
