What case is there to refuse a vaccine that is likely to add significantly more protection to the individual and community while remaining extremely unlikely to cause “other problems “?

It’s important to distinguish events that are likely from those which are unlikely. Otherwise you may mislead someone.

Note that the comparison is asymmetric. Forcing someone to do X is qualitatively different from that person not taking any action.

If the naturally immunity wanes quickly then that would be a good reason. Having said that, I do agree that advice and regulations around vaccination ought to be different for those who have previously been infected with the disease.

We can split hairs about which one wanes fastest, but it's not like vaccine provided immunity is bullet-proof or lasts forever: As of 10/4, COVID19 cases resulting in death or requiring hospitalization are up to 1/10,000 among the fully vaccinated and the trend has been going in the wrong direction for a while.

[1]: https://www.covid2020.icu/vaccine-breakthrough/