Just one of many reasons to read the cruise contract ALL passengers agree to:
"(c) The Vessel shall be entitled to leave and enter ports with or without pilots or tugs, to tow and assist other vessels in any circumstances, to return to or enter any port at the Master’s discretion and for any purpose and to deviate in any direction or for any purpose from the direct or usual course, and to omit or change any or all port calls, arrival or departure times, with or without notice, for any reason whatsoever, including but not limited to safety, security, adverse weather, strikes, tides, hostilities, emergency debarkations of Guests or crew, or late air, sea, car or motor coach departures or arrivals, all such deviations being considered as forming part of and included in the proposed voyage. Carnival shall have no liability for any compensation or other damages in such circumstances."
Also that a passenger can be booted:
5(b) Carnival and the Master each reserves the right to refuse passage, disembark or confine to a stateroom any Guest whose physical or mental condition, or behavior would be considered in the sole opinion of the Captain and/or the ship's physician to constitute a risk to the Guest's own well-being or that of any other Guest or crew member.
Carnival and the Master reserve the right to disembark any guest whose behavior affects the comfort, enjoyment, safety or well being of other guests or of any crew.
(a) Guest agrees during the course of the voyage to follow the directions of the ship’s Master, or his authorized officer. Guest further agrees not to solicit anyone on the vessel for any commercial or professional purposes. Guest agrees that any violation of this Clause may subject guest to disembarkation.