If HIV-negative men were more assertive about their status, they could take on a fairer share of responsibility in regard to HIV prevention. HIV-positive men have their own status to manage. It's not their responsibility to manage yours too, but it seems that they're expected to do so.
The danger of the "third-date rule" is that it allows for feelings to develop, albeit little baby ones. Disclosing your status once a semblance of trust has formed is like placing a loaded gun in front of a person and asking them not to shoot you with it. I prefer to avoid the firing range.