The Petri dish stuff is BS and can be largely mitigated.
No, not BS. Shared elevators, handrails, buffet spoons. Like nursing homes, cruise ships aren't where you want to be if there's a contagious disease going around. Even with "aggressive sanitation," norovirus outbreaks have persisted on cruise ship. See:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3294347/