They want to. Remember the 80's and 90's "AIDS is everyone's problem" campaign? They meant it.
Therein IS the problem.
They are sick, demented and depraved. The intend to infect is all with their disease.
Remember when AIDS was GRID (Gay Related Immune Deficiency), or the Gay Plague.
There is a reason throughout history that in any revolution the first ones killed were always the homosexuals.