>>I can't force someone else to not drink poison if they so choose but I surely can assert that it would be deadly to so do. The same goes for beastiality.
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>How will beatiality become fatal? How will it bring down society?
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>Question, if there is life on another planet, well having sex with an alias be a fatal activity? Will it destroy civilization?

It may, if we define civilization as "current order of law, order, property and production". IOW, if individuals seek pleasure outside of the ramification of their society, the society feels its members started voting with their legs, i.e. its ranks are growing thin. It rejects individuals who step out of its structure, and thus decreases the number of its own troops, so it's partly to blame itself. It does so because it feels there'd be more of those if the first visible ones were not punished (remember the elder's argument "imagine if we all did so-and-so"). If there were more, then some of the structure of the society would have to change in order to adapt to embrace these individuals. Then tomorrow some others would invent something else and the society would have to change again.

So yes, it can gradually destroy any rigid social structure. Now if we have a dynamic social structure, which can change itself and accomodate change in behaviors and still keep its stability, that's a different matter, and that's what we have today, more or less. Today's society has gone to lengths to include the rights of homosexual people, on one side, but yet goes to bigger lenghths to make sure some things wouldn't change (take RIAA vs Napster for example).