While everything you say is true, and I appreciate your comments, the reason the Destiny missed (substituted) it's port of call was because of propulsion problems, nothing to do with ship/passenger safety.
While I agree, you should never EXPECT to get to any particular port of call, I would expect the cruiseline to maintain their vessels to the capacity that they would have the ability to sail the itinerary that is advertised. Problems with the propulsion on the Destiny has been a rumored problem for awhile, and the issue should have been addressed long ago.
The fact is, Carnival did/does not want to cancel any sailings for an emergency dry dock to fix the problem. This would lose revenue for them. Is it right? From a passenger point of view, I say NO. From a stockholder point of view, I say whatever saves them money.
As a TA and stockholder, I am able to see the situation from both sides and appreciate both sides arguments. Personally, I no longer sail for the ports, so it would have been a non-issue for me.