Never heard nor read him to say this. If not the Dark Side itself then the Sith for sure.
Yup, tought the same.
Also as far as I know, it wasn’t retconed that red is unnatural colour for cybercrystals in lightsabers. You have to directly use Dark Side to literally wound it to bleed in red. If Force made object doesn’t reflect dark side naturaly, I dont think dark side is natural. But as I said, I quit years ago, lost track and not looking back.
But there is nothing in your first quote to support the rest of your paragraph. It’s just Yoda trying to emphasize that the force exists everywhere.
[ Luke ] : Vader… Is the dark side stronger?
[ Yoda ] : No, no, no. Quicker, easier, more seductive.
[ Luke ] : But how am I to know the good side from the bad?
[ Yoda ] : You will know… when you are calm, at peace, passive. A Jedi uses the Force for knowledge and defense, NEVER for attack.
[ Luke ] : But tell my why I can’t…
[ Yoda ] : No, no! There is no “why”.
Indeed, there is no why. In the OT there is just the objective truth that the dark side corrupts good men into violent tyrants that use their powers for domination, warfare and evil. The Emperor is the prime example of this, casually annihilating entire planets to make his mark. There is no balance there.
And that Life creates the Force
And destruction, death, emotions are all part of, integral and essencial parts of Life
But let this topic for to be a Man’ari topic, lets continnuse if you want elswhere about the Force and its nature 
Ah ye, the begining yes, I tought he said even the rest, maybe my misunderstanding. Whst he said directly in this doesn’t contradict statement that DS is cancer on the Force.
True.
Which happened to be written during time when Fel was just one of versions of Arcane (and also are present in only one letter from low level mage quest in Vanilla in canon, which took them directly from long non-canon WoW RPG).
I don´t think that the rules for Arcane, chaotic magic that coarses through veins of demons and was used by Aesir and Vanir Titans to shape Azeroth, can be applied to Arcane, cosmic magic of Order.
The cosmic chart and its consequences. . .
By now, a lot of this quoted scripture is heretical. Jokes aside, not a lot of it makes sense anymore and fel and arcane got their final divorce back in Legion.
I HATE COSMIC LORE
I HATE COSMIC LORE
I HATE COSMIC LORE
I DON’T CARE WHO THEY SEND I’M NOT GOING TO LIKE IT
Also… if it’s alright like that…
Prepare to be subjugated, vile demon!!! 
Welcome to the Dark Side.
We have been expecting you…
Not that I’m overjoyed, but still a step to the right direction 
Punishing demons for their crimes is definitely the right direction!!! You will bring me breakfast all the way to bed!!
(Altough I will still wait for the story to be at least on PTR, altough I believe they will be cleansed and not demons… who knows, my character would lose it’s idea if they would be demons.)
gahh star wars hisses
Is it still possible to use both Fel and Arcane?
Considering demons can use arcane spells, yes.
There was one failson demon hunter who apparently had problems but it seems like a skill issue to me.
Arcane can be used to contain the fel which is part of how demon hunter tattoos work but like Light, they do not play nice. Oil and water of magics. Order vs Chaos.
I was talking about warlock
I’d seriously advice against multiclass RPing as it gets very med’an to weild different magics all at once but there’s precedent of a former mage turned demon hunter using some basic arcane stuff in the class campaign.
I understand, I want my character to be mage who, even despite hating demons, just tries to use Fel out of curiosity and hunger for knowledge, but over years falls into it. So for some time primarily arcane but at some point switching to Fel. And I am starting close to that point, just geting some contact with some other lock and become thier apprentice and no Arcane.
Seems a natural evolution but consider also how warlocks aren’t just fel-heads and their spellbooks are full of everything from curses to Void and your baseline fire of Destruction is drawn chaotically from the Firelands. Wanting to study The Fel™ specifically for reasons is a very focused thing and not something to oopsie into.
You’d actively be going “this arcane isn’t enough!” which is fairly reflective of a common path to becoming a warlock. The spells are insufficient, the magic is too weak! There has to be a better way!