Here's how I see it. There are two things going on in Yoda's answer: Luke's fixation on the Force as a means to defeat Vader, and Yoda and Obi Wan's failure to protect Anakin from the Dark Side.
Luke is so new to the Force he's looking at it merely as a weapon. He's fixated on defeating Vader. Luke sees the Force as a tool and Yoda answers Luke at that level.
Luke asks the classic newbie question "which tool is better"? Yoda, being wise, knows that is a foolish question. A tool has good and bad sides. A foolish tool user will look for "the best" tool. A wise tool user will know their strengths and weaknesses and when to employ it. Yoda's quick "no" is dismissing the question. He answers the proper question, "what are the qualities of the Dark Side?".
Yoda: [The Dark Side is] quicker, easier, more seductive... easily they flow, quick to join you in a fight. If once you start down the dark path forever will it dominate your destiny. Consume you it will as it did Obi-Wan's apprentice.
Yoda gives Luke a simple answer because he does not feel Luke is ready to face all the complexities of the Force. Luke is old for a Padawan, emotional, and fixated on battling Vader. A Jedi Master like Mace Windu, with great training and control, can skirt the edges of the Dark Side. Yoda feels Luke cannot. Ben does, too. This plays out in the later scene where they warn him from facing Vader too soon.
Yoda: If you end your training now, if you choose the quick and easy path,
as Vader did, you will become an agent of evil.
Simple answer. "Do this and these are the consequences". Luke's acceptance of those consequences to himself to save his friends surprises Yoda and Ben.
Luke: And sacrifice Han and Leia?
Yoda: If you honor what they fight for... yes.
Ben: If you choose to face Vader you will do it alone. I cannot interfere.
Luke: I understand.
Luke's decision is still foolish and headstrong and risks the rebellion, but he is unwilling to sacrifice his friends for The Greater Good.
Yoda and Ben's training of Luke is colored by their failure with Anakin. Luke is Anakin's son. They were both considered too old for the training. They left Anakin under a corrupting influence (Palpatine), and have no intention of doing the same with Luke. This leads to some... creative protective truthiness. They mother Luke like a second child. Ok, they straight up lie to him about some things they don't think he's ready for.
Ultimately, in Return Of The Jedi, Luke does use the Dark Side to defeat Vader... but only just pulls himself back from being turned like his father. That glimpse of the Dark Side likely haunted him for the rest of his life.