A legal system can be faulty. (killing Jews was legal in the legal system of Nazi Germany)
An action is being undertaken by government towards a person against his will, whether you'd call this purifying the race or taxation to justify it is irrelevent.
If somebody steals your car (which is only yours insofar as government recognizes your purchase), there will be action undertaken by the police section of the government in order to return your car against another person's (thief's) will.
Compare that to Nazi laws too, maybe?
By Godwin's law you've already lost.
From a historical societal standpoint, it is also undesirable. Which begs the question: From what group standpoint is homosexuality desirable? I request a group standpoint because from individual standpoints, any number of arguments can be made regarding any topic.
Appeal To Belief
Without sources proving the undesirability from historical societal standpoint, the argument is baseless.
The existence of scientific law is itself evidence of creation. Laws of nature, matter, energy, fields are all evidence of creation for how else could these things have come to exist? Whatever brought these things into existence is what I term "creation".
The scientific "laws" are human approximations and generalizations of observations.
They by themselves do not offer any support to the idea that they might be created.
The lack of a common unified culture means people can only relate to people based on universal values. People often mistakenly project their cultural beliefs onto other people as universal values, taking them for granted. It leaves only our most basic instincts to relate to people with.
Ethnical diversity does not neccessarily mean lack of common unified culture.