But we are regularly reassured by officials and experts that, with our closed borders and quarantine, the coronavirus infection risk with the bubble is low.
If cruises were confined to Australasian tourists, perhaps tested before boarding, with reduced ship capacity and other safety requirements, it's hard to see why they wouldn't have a case to operate across the Tasman from a health point of view.
Is sailing around New Zealand and Australian ports any riskier than flying across the Ditch, and mingling with people in airports, hotels, shops, pubs and restaurants? Both involve elements of indoor and outdoor travel. Cruise ship cabins are the equivalent of hotel rooms or the inside of planes.
Even when on board and away from land, there are plenty of well-ventilated areas where people can find space on cruise ships, such as observation decks and outdoor pools.
The main hindrance is more likely to be logistical concerns in case of infections and pauses in travel.
Considering the bubble has yet to run smoothly, those are valid fears.
For would-be tourists, the main debate over bubble travel is whether it is worth it - given the potential for disruption and risk - or whether it should be avoided until after vaccination. Some might prefer to wait and save for travel elsewhere at a later date.
There is a question mark over whether the bubble is still sound, given India's pandemic surge which is now spreading to other countries; the low vaccination rates in Australia and New Zealand; and the occasional leakiness of both borders.
It could also be argued that it is a giant distraction from the vaccination rollout which, ideally, should have occurred first.
At least the Government, with the rollout, bubble, and now MIQ changes allowing more people in, appears set on gradual steps towards reopening. Slow progress is better than stalled limbo. Or the horrendous consequences of an error made in haste.
In that spirit, the bubble could at least be a time to test safety measures in preparation for regular voyages with vaccinated people.
Overseas, individual cruise lines are requiring passengers and crew to be vaccinated, and other protocols. Some are updating their air filtration systems.
The Norwegian Cruise Line threatened to boycott visits to Florida after the American state introduced a law stopping businesses from requiring proof of vaccination.
The United States Centers for Disease Control and Prevention is allowing cruise ships to conduct test runs to evaluate safety systems ahead of new voyages in the US and Europe from mid-year.
It said: "It is not possible for cruising to be a zero-risk activity for spread of Covid-19," and recommends that passengers and crew members get vaccinated.
Memories of the Diamond Princess disaster a year ago in which more than 700 people became infected and 14 died have made authorities extra cautious.
However, the extra safety requirements being put in place now are what travellers are looking for.
With the passage of time, and the expertise mounting up on prevention as well as vaccination levels, confidence in the cruise sector is increasingly buoyant.