The question of intent is interesting. On one hand a person knows they have HIV yet they choose to conceal it but for what purpose? Is it to deliberately harm their partner or just to have sex? In this context I see a difference when it comes to intent.
I think you are missing something here. To harm their partner and to just have sex is the same thing in this case. When one has HIV and knows it, to expose anyone else to it is to harm them. It would be no different to take a revolver with one round in it and spin the barrel then pull the trigger as you held it to their head.
Especially if that other person is not protecting themself. That is when the Positive person is obliged morally and legaly to speak up.
Precautions are not 100%, so even if the person is personally responsible they can get HIV.
The certain knowledge that ones potential partner has HIV will often be the deciding factor to say no for most people.
To my mind there is no argument. If you are Positive and know it you have the responsibility to inform all of your partners in advance if you are so reckless as to still be having sex with uninfected people.
It wouldn't be a question if it were typhoid, or heptitus, or almost any virulent deadly disease that passes person to person with contact.