I am not a chess master, but I believe the caution being given is not to only spend study time on openings and memorizing moves. While important to have an opening system, the meat of it, especially for beginners like me, lies in the middle and end game. You won't ever get any better at chess if you only memorize moves (as there are far too many to memorize). Happy studies!
Do not study openings ??

You don't need to learn any specific openings as a beginner, but you should become familiar with the Opening Principles: center control, active piece development (developing to squares where the pieces can be helpful), and king safety. I would also argue for a 4th one, keeping a good pawn structure (avoiding isolated doubled pawns), but that one is not quite as important at the beginner level.
You do not need to learn any real openings to be successful in chess. A good example would be the guy who got 1st at the IHSA State tournament last year. I was talking with his coach and he told me that he does not know any openings, but he just plays well enough to get out of the opening with a decent position and outplays his opponent in the middlegame and endgame.
Just learn how to play the Opening in general, and spend the majority of your time on middlegame and endgame strategy and tactics. That should take you pretty far.
Hope this helps!

the main problem is that they just memorize moves not the concept of the opening.playing the sicilian dragon and understanding it are two different things and also dont stick to the concepts like glue when opponent plays an out of the book move just stick to the rules devlop, control the center etc.
i saw my opponent do a minority attck in the sicilan agianst the smith morra in a otb game! he lost in 16 moves :) i dont remember the game though

Yes that brings up a good point: in chess there is an exception to every rule (except "don't get checkmated"). If you see a good reason to go against one of the opening principles, that's perfectly fine. For example, people tell beginners that it is bad to move the same piece more than once in the opening because this means that they are not developing their other pieces. Even at the top level they don't adhere to this "rule" all the time. Take the Ng5 lines of the Italian Game for example. White moves his knight at least two times, but Ng5 isn't a bad move.
That being said, only break these "rules" if you see a good reason to do so.

Thanks for your answers ! Yes, I know that trying to memorize is the best way to get in trouble sometimes, because, in some openings, the move order is critical.
This said, if engines know general principles and are strong at tactics, why do they need an opening database ?
And, BTW, has an engine ever refuted a line in a well known opening?

It depends on what you want from playing really.
If you want to improve your game and rating and become more successful then you should study all parts of the game, including openings.
However, if chess is more of a casual activity for you that you do because it is fun and you don't feel like investing too much time into studying then I think opening theory (which has gotten fairly vast and complex) can be safely skipped almost entirely.
That will mean you will run into the occasional opening trap, but you will learn to avoid them as you run into them.
I'd much more recommend studying some endgames because studying the middle game is more helpful if you understand endgames and what kind of endgame you want to aim for in the middle game.
Even for a beginner, studying the basic mates and how to win a simple pawn endgame is necessary. Otherwise you will find yourself in a situation where you have gained an advantage but are unable to convert it into a victory.
For someone seeking help with openings, I usually bring up Openings for Amateurs by Pete Tamburro (2014).
http://kenilworthian.blogspot.com/2014/05/review-of-pete-tamburros-openings-for.html
"Every now and then someone advances the idea that one may gain success in chess by using shortcuts. 'Chess is 99% tactics' - proclaims one expert, suggesting that strategic understanding is overrated; 'Improvement in chess is all about opening knowledge' - declares another. A third self-appointed authority asserts that a thorough knowledge of endings is the key to becoming a master; while his expert-friend is puzzled by the mere thought that a player can achieve anything at all without championing pawn structures.
To me, such statements seem futile. You can't hope to gain mastery of any subject by specializing in only parts of it. A complete player must master a complete game ..." - FM Amatzia Avni (2008)
"... For players with very limited experience, I recommend using openings in which the play can be clarified at an early stage, often with a degree of simplification. To accomplish this safely will take a little study, because you will have to get used to playing wiith open lines for both sides' pieces, but you can't eliminate risk entirely in the opening anyway. ... teachers all over the world suggest that inexperienced players begin with 1 e4. ... You will undoubtedly see the reply 1 ... e5 most often when playing at or near a beginner's level, ... After 2 Nf3, 2 ... Nc6 will occur in the bulk of your games. ... I recommend taking up the classical and instructive move 3 Bc4 at an early stage. Then, against 3 ... Bc5, it's thematic to try to establish the ideal centre by 4 c3 and 5 d4; after that, things can get complicated enough that you need to take a look at some theory and learn the basics; ..." - IM John Watson in a section of his 2010 book, Mastering the Chess Openings, Volume 4
The primary purpose of the 2006 book, Discovering Chess Openings, was to discuss basic opening principles, but, along the way, author, GM John Emms, did give some information about various specific openings, such as 1 e4 e5 2 Nf3 Nc6 3 Bc4. At one point, he wrote, "If you find an opening here that appeals to you and you wish to find out more about it, the next step would be to obtain an introductory text devoted entirely to that subject."
https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf
I know, this might be a well known subject...
I often see this advice given to beginners : tactics and middle game strategy are the most important points, don't waste your time working openings, it will only be useful later.
BTW, this must contain some truth, because it is often said by *strong* players !
However every good chess engine *has* an opening database. It means that tactics is not enough to find the first moves. And it is so frustrating to get a desperate position after 5 or 10 moves...
What would be the good balance between do it or not ?
(my kingdom for a knight, ha ha)