[Feel_Good_inc.]

that's a can of worms.
I'll try and keep it as rant free and calm as I can.

creative writing classes and courses can harmful to a writers skill. True on the face of it they do appear good. you have your writing looked at my "professionals", who really are either struggling writers themselves or they are writers who aren't able to live on the money made from their books and now are down to teaching what they know to survive, but still they are professionals who can look at your work and give you advice on how to improve. That's the face value.
Under the surface it's different. Learning to write is about finding the style you're comfortable with and what works for you. You learn, grow and develop in skill as you continue to write, check and rewrite your work. You develop your own standards, find your own bar and goals and level to reach. In a creative writing course you instead bring your work out and show it off to others when you are still learning your way through that creative jungle, when you may be slightly naive and a little vulnerable. You face criticism, packaged under the more friendly term of feedback not only from your teacher but, possibly also your fellow classmates who only know as much about writing as you do.
As your work is commented on you try and change it "develop" it so it matches the level and expectations of your peers. That's why it can be damaging. it's like throwing yourself in at the deep end when you're still learning to paddle. Instead of relying on your own judgement and using that to practise the craft and develop your skill you end up falling back on the judgement of others.
The key to good writing is to write for yourself, write what you like and enjoy to read. By showing off work in progress and receiving critical feedback you can destroy that skill because you will start second guessing yourself and think what your audience will like and try and write for them and the only thing you end up with is something that no one likes. least of yourself.

That's why I don't like creative writing courses. they can be more damaging to a writer than beneficial.

Writers develop the best when they are left to grow under their own power. you learn from your mistakes, develop your skill with every rewrite and learn and grow through the trial and error. You have to find your own path in the creative world, not walk in the footsteps of someone else. In that way, mediocrity lies. Most journalists take creative writing courses then end up working at newspapers because they never sold that "best seller."