Compulsion doesn't really work too well. Anybody with a life style that exposes them to the risk of infection from HIV is crazy if they don't do everything than can to reduce the risk, and inexcusably irresponsible if they don't ensure they aren't liable to pass it, including periodical testing.   Of course some people are pretty crazy and irresponsible, but that can't be helped.

Not that different from driving really - we have laws requiring driving tests, and insurance, and barring people with some medical conditions or a history of bad driving, and it still happens.
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The assumption people seem to have that sexual orientation is fixed and exclusive, and doesn't involve any possible element of personal choice doesn't seem to fit with the results of surveys. It appears that in the States at least there are rather more people who would describe themselves as bisexual as exclusively gay or lesbian, and that most people who have had some kind of sexual activity with members of their own gender wouldn't see themselves as either.

The implication of that isn't that people should be harassed into being straight, but also that it's wrong to go the other way and tell them that they necessarily haven't that option if they choose, just because they've tried it the other way..