blockchain does not reveal your birthname, homeaddress or anything else. thus privacy is not violated.
secondly, by linking a bitcoin address to your forum username is not breach either, as your forum username is not your real life birth certified name
thirdly if you doxx yourself by revealing your details which can then be linked to the forum name and or the blockchain.. transactions. then this is your fault
Trying to play devils advocate......what if you were to trade with someone privately your identity would be linked to that transaction and both the change address and the sending address. Couldn't the person you traded with leak this information?
couldnt you do a credit card transaction and the merchant(other party) then release your personal details and your credit card number. should you blame the credit card company that has not publicly released personal data, or the merchant(other party).
the answer is that you would say the person you transacted with is in breach of privacy, not the credit card companyunless the credit card company or the blockchain themselves hold and release a persons name, address of a person. its not a breach of privacy.
everyone knows the blockchain its a public ledger, just like its expected that you cannot blame a bank over privacy if you choose to use the ATM balance/mini-statement, and then leave it on a public street. it contains no name/home address. if you or another party links a bank balance or transaction list to your name. then that party that has linked your name is to blame.