I know a shot at me when I see one.
There is a WORLD of difference between I, an adult with a reasonably sound mind, choosing to wear diapers or training pants, and a young child who doesn't want to be potty trained. I can accept the difficulties and responsibilities of my choice and my actions. A five-year-old cannot.
While some of us diaper folk might sit around and say ''I'd let my kid stay in diapers and train whenever!'', that is not a decision a responsible parent makes. A responsible parent makes choices that are in the best interest of their child. They know, for example, that sending their otherwise healthy, just stubborn, kid to kindergarten in diapers is a poor choice. Not only are they basically marking their kid as a target for teasing and bullying, they're definitely going to raise the eyebrows of the school administration. Unless they have a medical reason, it's probably not going to go over too well.
Let's face it - unless the world decides diapers are better than toilets, potty training your kid at a reasonable time is the right choice to make. It's not fair to them not to teach them an essential life skill.