3D spotting = wallhack
The two reasons why I prefer hardcore servers is because I don't like 3D spotting and killcam.
Few minutes ago I killed an enemy I was unable to see at all because he was behind a thick black pillar of smoke. The only reason I was able to see and kill him was because someone spotted him. I was just firing at a moving red dot. I don't want that happening to me or others. If I don't see you... I don't see you. If I do... I do.
Same thing for killcam. Imagine you kill me from behind and because of the killcam I use the text chat or voice chat to tell my team/squad where you were few seconds ago. You won't like that. Sadly most "hardcore" servers in BF6 have a limited HUD which allows killcams and some 3D spotting.
The developers said BF4 inspired them but... they don't even know that hardcore shouldn't have killcams nor 3D spotting. What a joke.