It does appear to be the case that quite of lot of people are promiscuous, in the sense that they have sex with a number of stranger partners. In some cases the encounters are heterosexual, in others homosexual, and for a significant number of people both.

And of course there are also a great many people, who are in lasting relationships with a single person, heterosexual or homosexual.

This means that a register system restricted to gay people would be irrelevant. It would be too narrow and too wide. It would not take in all those at risk of catching and transmitting HIV, and it would include others where there was no such risk.

Anybody with a "promiscuous" lifestyle, more especially one involving unprotected sex would be very foolish and also irresponsible not to be regularly tested. But that's how some people are. But to assume that there might not be many who would wish to take advantage of such a scheme, is not necessarily right. People with a "promiscuous" life style should not be assumed to be stupid and irresponsible.