First, societies which have their basic moral tenets and their mores undermined often are the ones that are on the verge of collapsing.
Well, that pre-supposes that culture and societies are static constructs to begin with - which, incidentally, is absolutely false. Cultures are constantly in a state of flux, including their values. Societal norms in 1600 differed markedly from societal norms in 1700, which in turn had little in common with societal norms in 1800 and so on and so forth. Unchanging, static tradition is, for the most part, a fiction.
Socially, if we allow ourselves to become too fractured we can no longer function as a powerful political entity. We can no longer have the sort of fusion within society that is needed for real success and real cultural creation.
You do know that the concept of the nation state and the nationalist ideal that supports it are relatively new, historically speaking - don't you?
Look back into history and see how the fall of most civilizations are marked, socially.
Most of these downfalls could be traced back to a phase of militaristic empire-building, in which the culture in question overextended its reach and weakened itself to the point of collapse. The very economic overabundance of wealth that allowed such societies to become increasingly "decadent" was merely a consequence of such expansionism, not its cause.
That we consume more than we should, by the way, has been an integral part of capitalism from its conception onwards. For the last few hundred years, we've managed to stave off most negative side effects by delegating them to economically dependent "developing" countries (or, historically speaking, colonies). It's only now that the consequences of our wasteful lifestyle finally start to catch up with us.
Do you ever think about the society as a 'social collective' and the sense of obligation we have to one another as individuals?
Of course I do, although I'd extend that sense of commitment to the species as a whole as well, and to the welfare of the ecosystem that sustains us.
Slave owners said the same thing? Yeah, I guess they would say it 'undermines society.'
A lot of groups have said that.
Could you please tell me what slavery and homosexual marriage have in common that you can draw this comparison?
This has already been answered: a powerful majority tries to curtail the rights of a minority by pointing to religious writings as a "confirmation" that God wants things to progress like they always did. And yes, the slave-owners had good biblical support for their stance. I'd even go so far as to claim that it was better than the current anti-homosexuality angle.