The people expressing this thought clearly have spent very little time in other countries to appreciate what y'all have.
Also a bunch of other examples where the countries aren't necessarily the best to live in, but pretty much everyone is happy they split - Yugoslavia, India/Pakistan, West Pakistan/East Pakistan. Singapore/Malaysia (to be fair Singapore were kicked out).
A split of the US among the crazily politicised duopoly wouldn't be the end of the world. One part would be reactionary as hell and move time back (on social and ecological issues), the other.. who knows.
The US in many ways legitimizes itself as a government in the traditional of the "western european project," by evoking the ritual, esthetic, ideals, and historical lineage of ancient Greece and Rome. From names and architecture, to values and ritual, there is an establishment of ties, real or imagined to be real.
On one hand, this works fantastically to mentally cement the US in the greatest of greats, but we cannot ignore the visibly obvious - that ancient Greece and Rome declined and fell. By drawing a parallel to ourselves(us-centric obvs) we draw a parallel to our own decline. We we're honest with this comparison, we have to be honest about the demise of these governments too. It's not possible to separate the too.