It's the responsibility of each user to protect their own system, not to protect everyone else's.
So you would send a virus to someone you know and not care? How selfish.
If you knowingly ignore the fact that you may be sending malicious code to others you may be guilty of a crime. Either way you will be setting yourself up for a civil suit for damages.
I saw an coworker once get fired on the spot after infecting another workers computer and expressing the same sentiment you have to his boss. I have also seen a college student kicked out of school for infecting others through their negligence and refusal to use any method to prevent this. I have seen a person get into serious legal trouble for infecting an important system when they should have known better.
It is every users responsibility to avoid infecting others with malicious code. If a user has any reason to suspect they are infected but fails to act upon it and then transfers it to others they are being negligent.