2. Once you transmit your key over the internet to "use" it legitimately in the blockchain to send Bitcoin, although encrypted, it is subject to capture and hacking.
In order to show this point valid, you would have to show that your
public key is significantly more vulnerable than your address.
Your address becomes a part of the blockchain as soon as you receive bitcoins at the address. It doesn't matter if you "re-use" it or not. Fortunately the private keys are protected by 3 layers of cryptography (and no encryption at all).
To calculate a private key from a bitcoin address:
[step 1]
[step 2]
[step 3]
At the moment there is no known way to reverse ANY of those three functions, so it doesn't really matter how many attempts the hacker uses.
The OP was arguing that when you use an Bitcoin address to send BTC, you eliminate your steps 1 and 2. The counter argument is that step 3 is so difficult that it doesn't matter.
3. With common virus distributed key stroke loggers (etc.) your copy and paste of the private key to use it, could be detected compromising your wallet security.
If you have a key stroke logger, then your entire wallet, along your your banking login, if you keep that on your computer, is compromised. It doesn't matter how many Bitcoin addresses you have at that point.