They had previously set the groundwork in Romer v Evans, Jen.
http://en.wikipedia.org/wiki/Romer_v._Evans
http://en.wikipedia.org/wiki/Romer_v._Evans
Quote:Finding that "laws of the kind now before us raise the inevitable inference that the disadvantage imposed is born of animosity toward the class of persons affected," the Court inferred that the passage of Amendment 2 was born of a "bare...desire to harm a politically unpopular group".[2] The Court added: "[I]f the constitutional conception of 'equal protection of the laws' means anything, it must at the very least mean that a bare ... desire to harm a politically unpopular group cannot constitute a legitimate governmental interest."(emphasis added)[