The longer I work as a programmer, the more I say "trust no one"
Yes, the publishers should have made a well-formatted file, and all the users that learn ePub for the first time and make it in Notepad should never make mistakes - but they will. And since it's possible to make such a random invalid ePub generator as I described, and use it to test the software, should one refrain from doing it on moral grounds? (ie. that documents should follow standards).
No one is saying about silently ignoring errors, you can refuse to open such invalid book, print out 3 pages of errors in a special window (would be even better) - but crashing the device? A bit over the top
