Even in English, most people prefer to distinguish between upper and lower case, particularly with respect to names. I don't like having my name, e.g. in a salutation, in all upper case. Would you be happy to have your mail, documents, ..., use phiL factoR, or perhaps use other random capitalizations?
However, I remember back in the Teletype days that we managed to survive with only upper case - so we could go back to
https://en.wikipedia.org/wiki/Baudot_code#/media/File:International_Telegraph_Alphabet_2.jpg
and do  away with lower case, accents, ...

Regarding Unix/Linux, nobody is forcing you to use mixed-case file names. Just don't do it. And if  you are working with data which has mixed case information, most Unix/Linux commands have a case-insensitive option (often -i).