Is polyamory the next liberal step or things "were always that way"?

So...tinfoil hats are on!

Ok, society has successfully ruined the institution of marriage, if by desire of some institutions or not is a whole other topic. The fact is that we there is no scandal in divorce and remarrying, two, three, or a dozen times. A lot of people don't even think about getting marriage, as they feel like they don't want to "attach" to anyone, and as having sex outside of marriage became more and more acceptable, it makes sense (in a materialistic view) that things would go this way.

However, we still hold very strongly the institution of fidelity. A couple expects faithfulness from one another, cheating on your partner (married or not) is generally viewed as a big thing, often leading to break ups.

So...it seems like that anyone interested in destroying the institution of family should take the next step to try and destroy the institution of faithfulness. Hece: polyamory.

I don't know about the US, but in Brazil it is already starting to have the usual movements of being propagated by the media as "this trendy new thing that open-minded people are doing. What you think about it? What is your opinion?" which is usually the first step of this process.

So...opinions? Am I seeing ghosts here, or this looks like the gay marriage pattern all over again?