Not an assumption. Before Covid, no one was excluded from going on a cruise. Now families that are not "vaccinated" including their children are excluded. Pretty simple. I noticed you didn't state how many people were actually on the cruise you went on, just how many people joined a Facebook group. The cruise industry is dying on the vine right now. I was on a cruise in Mid October and am going on another one for Thanksgiving. The prices are the lowest I have ever paid in 25 years of cruising and they are at less than half capacity. This will not increase business.The error in your assumption is that this only EXCLUDES people. It does not. There are people waiting for vaccines and mandates before they will cruise. This move actually INCLUDES more people that previously did not feel comfortable spending their money to cruise.
Some people will cancel. Others will now book. This isn't going to have a detrimental impact. I was on one of the first Dream cruise back after they added a vaccine requirement for 12+...literally the day they announced vaccines would be required, dozens of new people booked and joined our cruise Facebook page, so excited that they can now cruise. The number of people who joined those final 2 weeks was monumentally higher than those that bowed out.