I understand that reusing the same wallet address is not advisable when security is the top priority, the last time I read public can be share online but what you just said now makes me surprise and curious what you really mean. The question is why would people with exposed public keys be vulnerable?
On the similar vein, reusing address results in exposed public keys as transaction will contain the ECDSA public key of the address.
The private key can be derived from the public key using Shor's algorithm given a sufficiently powerful quantum computers. Addresses are not public keys, they are the hash of the public keys.