>>/78970/

No I'm not a Dr or an MD but Dr. Robert F. Cathcart M.D
and Dr. Klenner, MD are and used high dose vitamin C successfully.
Some of their results are described in the first link in the OP

links in your post are to scientific studies showing
a high intake of vitamin C supplements can increase risk
of kidney stones for example:

https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/1568519

> Results
> During 11 years of follow-up we ascertained 436 
> first incident cases of kidney stones. Ascorbic acid 
> use was associated with a statistically significant 
> 2-fold increased risk (Table). In contrast, multivitamin
> use was not associated with kidney stone risk (RR, 0.86 [95% CI, 0.62-1.19]).

and what is the baseline risk of kidney stones?

https://www.uwhealth.org/urology/how-common-are-kidney-stones/11208

> The lifetime incidence of kidney stones is nearly 13 percent in 
> men and 7 percent in women.

So a high intake of vitamin C supplements over your entire life
would cause an additional 10% risk of experiencing one incident
of kidney stones.  One would assume that short-term high intake
during times of illness would cause a proportionally smaller risk

Its up to each to decide whether the risk is worth the benefit.

Let me finish by pointing out a critical part of the protocol for
Using vitamin C to fight an illness, and that is using a timer to
maintain a regular dosing schedule throughout the day, and to
take as much as you can tolerate WITHOUT diarrhea.
This link also has a table of doses that Dr Cathcart ( yes, MD )
found effective for various illnesses.

http://orthomolecular.org/library/jom/1981/pdf/1981-v10n02-p125.pdf

> It was found that maximum relief of symptoms, the most shortening
> of the course of the disease, and the greatest reduction in complications 
> could be obtained by the oral doses just below the point causing diarrhea. 
> This titration to bowel tolerance is usually easily sensed by the patient. In 
> many conditions symptoms are markedly suppressed but will return rapidly 
> if the dose levels are not maintained long enough. In the case of very toxic 
> diseases, doses may have to be taken every half hour. Even short delays in 
> taking these doses may prolong the disease.