You seem to be arguing that any activity that is harmful is immoral. At least, that is what I understod you to mean when you said:
Consideration of the consequences of homosexuality (which are perfectly predictable in every society) can be used by societies to invoke natural law to suppress it, simply by reason of the predicted and known consequences (plenty of biblical and historical examples). This is why even atheist / shamanist countries have had strong laws against homosexuality.
Is that the case? Do you think driving a car for leisure is immoral? How about skiiing, horse riding and rock climbing?
Or have I misunderstood your argument? If so, please clarify.