Lord Krsna, that's a lot of words that don't come anywhere near addressing what I actually said.
The root of this is that you're assuming harm or impossiblity where it was never explicitly stated.
No, see, you're projecting. You outright state that you assume it's possible, so you conclude that disagreeing with you must mean that I'm assuming the opposite of what you are. But I'm actually criticizing you for assuming a conclusion at all.
I have reasons why I suspect it's impossible without Raava, but the proposal of a hypothesis & the expounding of the reasons behind it is not the same thing as claiming that explanation is the definitive truth.
The root of the matter is that the lion turtle stated it had never been done; that's it, that's all.
Okay, so if the Lion Turtle was not suggesting that it could not be done or would be dangerous to try, why not give it a shot?
Doesn't make sense, does it?
Their discussion during his training was about transfer and the dangers of transfer, not about danger in holding multiple elements.
Maybe, before you start trying to argue against things that I never said, you should actually address at least 1 thing that I criticized you for ignoring. Just a thought.
Additionally, you're still making unproven assumptions about Raava's effect on the Avatar just because they were bonded. Wan felt a rush of power from Raava, that was it--a rush that seemed to die the moment they were separate again.
Actually, Korra was also heavily wounded & passed out at having Raava ripped out of her. It's unclear if the process of extracting her caused these wounds itself or if she still felt the attacks that Raava were hit with, but either way suggests that the long term bond affected Korra's body in SOME way.
The flaw in assuming Raava would have a lingering effect (thereby allowing the Korra to hold four elements unaided) is the after-effects of their separation: Korra lost all connection to her past lives (never to be regained); she couldn't even sense Raava's presence, despite searching for her. She lost all that, and yet somehow, you believe that holding four elements is the sole after-effect despite 10 millenia of unity. It doesn't fit.
You're assuming--since I see how much you love that word--that these all work on the same mechanics & therefore would be affected in the same way. However, we saw that each time Unalaq struck Raava, a past life was lost. So, let's try a thought experiment:
What if Unalaq had stopped after the 1st hit & allowed Raava to re-enter Korra? It is reasonable to infer that Aang would be lost, but there would be no other effects. The other past lives would still be able to be accessed, Raava would still be able to communicate, & Korra could still bend all 4 elements & go into the Avatar State.
The point being, you cannot safely assume that if Korra loses some of the abilities that Raava gave her access to, she should automatically lose them all, & whatever remains is something that a normal human could do. If Korra's spirit works the same way as her past lives, then it's plausible that she still carries some tiny piece of Raava's energy, & that could make all of the difference.
What we don't know is whether it is specifically impossible to bend multiple elements, whether from physical or health limits.
And because we don't know and it was not stated, it's perfectly reasonable to conclude that bending four elements is neither unsafe nor impossible.
Goodness, so close, & yet so far. Okay, the problem here is that you are referencing "failure to reject the null hypothesis," but not understanding that "failure to reject" does not mean "accept." As I said in the beginning, this is your core problem. Everything must be a binary yes or no to you, but that's not always how it works.
"I don't know" means just that. It is not a synonym for "it's not true," & there are so many examples as to why that's a ridiculous argument:
Haven't found a cure for this disease, there must not be one.
Don't know if there's life on other planets, must not be.
Don't know if there's anything beyond the observable universe, must be nothing.
Don't know if I'm being sarcastic right now, clearly I'm dead serious.
Your notion that I can't simply say there is no definitive explanation, that I have to assume 1 or the other, that's just absurd.