If all the other demographics a able to regulate their behaviour to take account of HIV, why not MSM?

How do you know they are not regulating it? A few/some/many/most? Self-evident, is it? All in the numbers, eh? What more do we need, eh? How do you know that the situation might not be a lot worse but for many gay people regulating their behaviour? You haven't a clue. This is a groundless, broad-brush stigmatisation of gay men. No surprises there then.