The parent is surrounded by family who can review his writings.
The non native English speaker with poor spelling knows first hand that he needs his resume to get reviewed. And he should not expect to easily find a highly qualified job that requires to write English in an English speaking country if he can't read and write English.
So far, your examples only manage to show that people could manage just fine and if they can't they were not qualified for the job.
English is not a rare skill. There is no shortage of people who can write decently.
The spelling heuristic gets rid of between 5 and 20%, right away. A lot of those resumes would also be caught by other heuristics (no ten page resumes, etc). Most of your concern cases would also fall to my other filters as well. And quite frankly, if a resume jumped out at me in a positive way, but it had three or four or five typos? I'd interview. It's not a hard and fast rule.
It's not as black and white as you think it is.
It's a relevant filter and it's a terrific value for time.
A good old exercise to print number from 1 to 100 and then 100 to 1. That's the sort of things that get rid of half the candidates.
A first-generation college grad paying their way through school by working full time in a new town.
A single parent trying to get into a field while working and caring for their family.
A non-native English speaker who perhaps understands the general structure of the English language, but not the nuances of grammar (or what is expected in a Western CV/Resume).
I hope you could see that your earnest appreciation for proper spelling is unfair to apply in such a black/white dichotomy. I kindly ask you to reconsider your approach.