I tried to read the para 3 you pointed to it actually blew my mind it explains about subgroup attacks but look at the forum and bitcoins users why do they still post their BTC addresses publicly?

It means no one can able to calculate and find the private key of any public BTC addresses have you tried to search it through Google? You should find something like this "it is impossible to derive the private key from the public key".

And please read this "Technical background of version 1 Bitcoin addresses"