I'm saying that an arbitrary number of exact replicas of a master can magically appear on the network believing they are the one true master, identifying themselves as such, and expecting to act that way. Additionally, an arbitrary number of database masters expecting to participate in the cluster may show up or leave at any time. That is somewhat nontrivial for even modern databases to deal with.
Why run your database inside kubernetes though? We've always white gloved our database (and a few other special services). You don't have to put 100% of your infrastructure in docker/kubernetes.
If you're running multiple copies of anything that cares about the concept of a master it better have its own consensus algorithm. Luckily such things exist and are open source.
