If a person consents to sexual activity knowing the partner is HIV positive, that consent is an answer to any criminal charge in respect of which the Crown must prove the absence of consent. Those charges would include assault, sexual assault, aggravated assault, and aggravated sexual assault.
However, there are many such offences, including attempted murder, that do not require proof of the absence of consent.
Anyone who intends to kill someone else and does something beyond preparation to bring that result about, is not morally blameless, but rather a would-be murder who is properly accountable under the criminal law. A complainant’s consent to have sex with a person he knows is HIV positive does not negate or vitiate any essential element of the offence of attempted murder.
It is very unlikely, however, that a court could find that an HIV+ accused who had sex with another person had the specific intent to kill (which is required for the offence of attempted murder), as intent to kill requires a finding beyond a reasonable doubt that either:
1. the accused’s purpose was to kill another (either as an end in itself or as a means to achieving some further end), or
2. the accused decided to commit an act believing, to a virtual certainty, that the act will cause the death of another.
R. v. Boone, 2019 ONCA 652