Actually, not. Sorry, but married couples who swap partners are not following the norms of our society. I am not talking here so much about the details of a married couple's intimacy together. But the fact that they switch partners is weird. Why marry? Why have children when you are going to expose them to such? In fact, these folks are now missing a child, possibly because people following their lifestyle had access to their home. I realize we do not know what happened to Danielle, and this could be proven to be wrong. But it still remains a possibility. And these children have continual exposure to immoral parents.
Not following Societies publicly accepted norms is hardly the definition of evil. I make a point to say PUBLICLY because the number of married individuals engaging in sexual activities outside there marriage is higher than most will every publicly admit or realize to anywhere from 1/3 to 2/3rds have cheated depending on the study. Open and/or Swinging relationships have been around long before this country, and will be around long after its gone.
As to why marry if you going to have an open relationship sexually? You would have to ask those engaged, but I would bet dollars to dougnuts you will find reasons as broad as the rainbow. My guess would be they for their own reasons have decided to spend their lives together, relationships are far more than sex, at least to anyone with a maturity level above 18.. in fact that's overall one of the lesser qualities that will ensure a long term relationships success.
Now as to exposing the children to such, this is where you really are losing me. Exposing them to what? No one has alleged they engaged in their activities around or in front of their children. (Assuming they even were swingers, which let us not forget is nothing more than a rumor at best at this point) If this couple got their jollies going to clubs and having casual sex with others, I don't have to agree with it, but I don't see how this alone exposed their child to something evil. No more than the couple who goes to the bar every once in a while. I think none of us live adult lives with no adult content that children should not be exposed to... but just because we do things as adults when children are not around does not mean that we expose our children to them simply by the fact we did them... this seems a bit of a stretch to me.
Now, I will be the first to condemn these two if they indeed were bad parents, and if their sexual picadillos put their children at risk, I will definately be all over their butts. However, as of yet there is nothing other than rumor and speculations... Something definately does not smell right with this, but I will wait before I condemn them as bad parents to at least hear something that isn't rumor that shows them being bad parents.