Its idea is simply that error is just state like any other. I find that to be quite reasonable – and something I miss dearly when I work in other languages which try to get overly fancy to try and hide that fact. There is nothing special about errors. The machine certainly has no concept of errors. Why does it need special constructs?
Bad practices like assuming T and error are dependent do break the ideas, but a language can only hold the hands of poor developers so much. Someone determined enough to write bad code will do so in any language.
Realistically, if there is a handling problem, it is a problem for all values of all kinds. Every single problem one can point to about handling errors is also a problem when handing names, email addresses, random numbers, etc. To single it out as an error handling problem specifically is flawed.
> I have quite strong feelings on the subject that aren't fit for polite discussion.
I'd love to hear more. You won't hurt my feelings. Getting worked up about a programming language discussion is illogical.