The main problem with the "discrimination" against homosexuality rests in something far deeper than just free speech. At the formation of the USA, even Christianity as a base religion (the basic tenets of Christianity) could not be used as a means to determine what is right and wrong, as there are many sects of Christianity -- all claiming to be right. It was therefore determined that the U.S. as a democracy could not be allowed to become a theocracy (as had happened in many countries in Europe.. though perhaps not in name.. they answered to the church.. and therefore were in effect.. theocracies of a sort), as any sect might turn the country for its own personal gain, and persecute those in other sects -- leading the nation away from what may be the truth, yet happens to not be accepted by this dominant sect.
With this as background, the only course of action available to the founding fathers was to base the constitution on commonly held moralities which were not only reperestened in at least a majority of the Christian sects, but determinable from easily evaluatable means such as a simple observation of the detriment an act causes society. When such a link can be established as true (or at least agreed upon to be true by a majority or perhaps great majority), one can easily state such an act to be a criminal one. Yet since a criminal act is also an immoral one (against true morality), then we can assume that all amoral acts are, in one way or another, criminal. However, the only perfect standard by which morality can be legislated is in the case of a perfect ruling body who can state unequivocably what truly are the morals which should govern a society. In the Old Testament times, this was accomplished by prophets -- who were told directly by God what was right and what was wrong.
Now, since we are in a time when no perfect ruling body (who can determine all morality and criminality perfectly) exists in our land, save the power of God, Himself, we are stuck defining these moralities and criminalities only where they can truly be measured. And therefore, since homosexuality, though expressedly forbidden in the Bible, *is* a moral issue and extremely hidden in its detrimental effects to society (as what one person may see as detrimental may not be seen by another as such), homosexuality shall not ever be accepted in this country as a criminal act (though adultery is still tagged as such in some states). Likewise, fornication shall never be accepted by the country today as a crime, as only crimes which can be directly shown as always detrimental to society will be labeled as such.
In conclusion -- any issue whose morality is more than slightly in question by the general public at large may be designated noncriminal if there is a lack of evidence linking that issue to any detriment in society. This means -- as happened in many countries that rose and fell -- we shall, as a country, tumble further and further into the abyss of immoral behavior as the limits on these seemingly nondetrimental acts continue to drop based upon our own choices as a people to covet immmoral behavior. The remaining issue is determining what is actuality to be labeled criminality (against a law) and what are simply human-made-mistakes that requrie no punishment.