Calling suing an airline for switching a seat silly is abuse? Oh dear... Good thing my wife has different notions of abuse, or we'd both be in the slammer for aggravated spousal abuse (battery?) a while ago.
As I said in my previous post, without spelling it out fully, the part about 'security' and 'safety' reasons is there just to make the policy look nice and justifiable. 'Operational' covers anything and everything else - the airline does not need to make an appeal to security reasons or to justify their basis with a safety rationale. We decided it'll be easier to serve this family if they're seated together - that's operational. Is the deck stacked? Yes.
Next - I only said that actually seriously considering suing is silly, the threat of suing can be a smart tactic to put bozos in their place. It doesn't even matter if you will sue or not - they're just looking for an easy target, as soon as you make yourself a difficult one, they'll simply move on to easier fruit. As I said, not at all facetiously, confrontation sometimes works. And yes, Emerald status helps a great deal. There is no doubt that a complaint by an elite member is something an airline employee would prefer to avoid.
Finally, there definitely is such a thing as an unenforceable contract, or clauses of an agreement that cannot be enforced because they run afoul of consumer protection laws or whatnot. That said, it usually has to be something pretty egregious - witness how long it's taking Congress to do anything about various banking and lending practices, particularly with credit cards, that in some cases are clearly predatory. And people are talking and talking for years - nobody is suggesting that the contracts simply not be enforced. And all in all, that's a good thing - once rules don't exist or can be bent, even bad ones, it's an awfully slippery slope to total anarchy that benefits no one.