To help me articulate better, I’ve chosen to illustrate your generalization in this case: a person who is infected with the HIV virus, who chooses to not inform their sexual partners of their status nor use any barrier-based contraception (female or male condom).
To me, this is assault, and should be dealt with in the exact same manner. Calling police and pressing charges, for starters, as well as a suitable punishment for the person who infected others. The person has done an action which was non-consensual with the party involved, and this infringes on our basic rights to life and liberty. In the case that a person would WANT to be infected with the virus, the infector should not be punished as it is a consensual act between the people involved.
Least of all, this person would no longer be a friend. I am not friend with people who have no basic respect for one’s right to life and liberty. I would then take steps to inform others of this person’s choice, such as informing any of my friends who might want to have a relationship with that person. I would then cut this person from my life completely. Life’s too short to deal with crappy people like this.