If it is more common for functionality to be broken in an SPA than in a non-SPA, then that most certainly _is_ a valid argument against SPAs (from a user perspective). It's not an argument that all SPAs are bad. Rather, that I prefer non-SPA implementations because I can generally assume that it will have fewer bugs/annoyances in using it.
Why not? "You have to reimplement a huge amount of current and future behaviors that just work for MPAs" is definitely an argument against SPAs. That's extra work, extra potential for bugs, extra potential for accessibility problems.
It sort-of is if bad developers are less likely to wreck havoc with MPAs. Also, I don’t think that back-button breakage automatically indicates incompetent developers (although I tend to swear at them).
