#1. security. When you make a bitcoin payment; that one payment address then forever connects you to your wallet thus allows the receiving person to see all your previous receives/sends, and, all your future receives/sends. Any payment you received, or spent, then crushes your anonymity. You are forever outed; fully exposed. Really, it's no different than everyone in the world watching your bank account; seeing all the payments coming in and going out. Bottom line is you can never send or receive a payment to anyone in the real world. Your bitcoins/activity will forever be linked to you. Chainalysis perfectly lays out the problem.
all transactions in bitcoin are of course public in nature because they require a blockchain network, as we know bitcoin is a digital coin like electronic currency and of course all transactions in bitcoin require a chain network such as blockchain to record all digital transactions that are public, even many sources conclude Blockchain as a digital book that has a data-based technology system, but its security must be reliable because it is protected by complex blocks and passwords.
Therefore, in my opinion, bitcoin security is not from transaction records that are digitally listed but from their respective holders and of course transactions against bitcoin will be safe as long as we don't use them for criminal acts.