Agreed, but a tactical error in the opening is replicated and multiplied throughout the game. if I'm going to criticize it as an abstract strategy game, it's too sensitive in that regard. Yes, an error is an error, that's why they're called as such. In chess, opening errors have much more drastic consequences, depending on the error, than say Go, where you have more opportunity to recover from the error. An opening tactical error can spell doom for your middle game and end game (as analyzed by chess commentators, instructors, books, videos, etc.).
Outside of amateur casual play, you must play a stronger opening game than your opponent, if you want any hopes of winning. Even if your mid and end games are stronger, if you make a tactical opening error, you may never get the opportunity to play that genius finale, because you'll never get the opportunity to recover. Openings have to be damn-near perfect when playing seriously. That's what bothers me.