I'm just trying to say that's what the posters responding to you are talking about. It's been talked about for a long time on the Boards to not count on the covid policy in place because at any point in time it can be changed or revoked entirely.
As far as going backward Carnival company (includes more than just Carnival) for Australia and New Zealand routes requires masks for passengers at the moment, routes all over the world may be subject at any point in time for adjustments in their protocols either by a cruise company or the port/government, it is a risk we all take. ETA: and it was mid-cruise for at least one Seabourn ship several weeks ago where they were in New Zealand waters headed towards Australia (this was at the end of a 65 day world cruise) the next day
The uncertainty is out there in terms of what a cruise company may choose to do and that's all the initial poster was trying to get across. And now there has been a recent change in so much that your point of "well I'll just cancel for covid symptoms" is no longer valid for bookings after the December date for DCL which was bringing in my comment about future bookings.
You ultimately choose what you want to do, no discussion on that aspect of course.