Also
@lynde what he actually wrote: "I was born with a definite pervasive melancholy . . .what frustrated me most in the last year was that I had built no ties to family or friends. There was nothing of lasting worth and value. I led a detached existence and I was a parody of a person - literally and figuratively. I didn't tell jokes - I was a joke".
He wrote of perception, not necessarily reality. When it comes to friends, he is saying in the past year, he feels he "built no ties to family or friends" and that he was "detached" a "parody of a person."
This John Doe clearly had family as he mentioned them when addressing the letter. Depressed people can sometimes mask quite well, so he may have had any number of friends, at least on a surface level, even if he felt like a "parody", and someone who "never developed into a real person." Of course he also may have been a complete loner as well.
IF the Belle Chasse UID is possibly Earl Joggerst, he left home in August of 1972. Which also would give a few years for things to change socially--meaning the original group he left home with to split up and go their own ways--and for any mental illness to develop. (Typical pattern, would think the stress of life on the run would make it worse. IMO)
He was 15 when he left home, and would have been 17 when the Belle Chasse Doe died.
I am not saying Earl definitely IS this John Doe, only I would really like it to be ruled out.