My rebuttal would be that the beliefs they follow are taken from the Bible, the same text many mainstream religions use. Christians believe in the teachings of the Bible which condemns homosexuality, they are one in the same... one just picks and chooses what to follow from the same teachings.
A lot of mainstream Christians who are not considered a "cult" do the exact same type of protesting at abortion clinics.
See how if all religion just disappeared we would all be better off. In fact 9/11 would have never happened.