It breaks the internet because it breaks IP - the internet protocol. Segregating devices onto separate networks that are not routable to each other is something

It breaks the internet because it breaks IP - the internet protocol. Segregating devices onto separate networks that are not routable to each other is something that reduces the overall functionality of the internet, not enhances it. It doesn't help that it's a shitty hack which causes endless lost time either spent wondering why something is broken, or through designing entire protocols just to get around it.