Originally Posted by You
NEVER...NEVER...go anywhere on foreign soil without your passport!!! If you are stopped by the police or need to give proof of ID, almost all countries will not accept anything but your passport. Without your passport with you, you are considered no more than an illegal alien...subject to possible jail and deportation. Even the local US consulate will not help you without proof of citizenship!!
Your point about needing a passport to present as official identification is true of some countries but not all. Nonetheless, all U. S. Embassies and U. S. Consulates will act to assist you if you present yourself and provide verifiable information (name and date and place of birth or naturalization, for example) as to your status as a citizen. Indeed, one of the functions of U. S. Embassies and U. S. Consolates is to issue a temporary passport that permits you to return to the United States if you lose your passport in a foreign country!
Beyond that, "kd" is quite correct.
>> 1. Cruise ships often collect the passports of all passengers so that they have them available for immigration staff when the ship enters a foreign port. If you wish to keep your passport, you will have to appear in person at "oh-dark-thirty" when the ship arrives -- that is, if the staff allow you to board without complying with their instructions!
>> 2. Some foreign countries have laws requiring hotels therein to retain passports of foreign visitors from check-in to check-out so that they can present them to authorities if authorities question the identity of a guest. Of course, this also (1) prevents foreign visitors from leaving the country without paying their hotel bills and (2) provides authorities with immediate identification of any guest who leaves the hotel without paying!
More fundamentally, the cruise lines know the requirements of each nation that a ship will visit and provide appropriate direction to their purser's staffs with regard to passports. I have been on cruises during which the staff collected our passports for several ports of call, then returned them to us for a couple ports of call where we had to bring them ashore, then collected them again for the duration of the cruise. It all depends upon the laws of the countries that each cruise visits.