It's not a matter of being (im)polite.

I do not believe any developer in this world really wants to deliver software that leaves end users helpless... software that a user cannot even launch after it is installed.

I assume - and I'm pretty certain about it - that developers who go all the way from coding, uploading to -devel, taking the input from -testing and finally promoting their package to Extras, that such developers want to deliver perfect user experience for non-geek end users. Otherwise they'd put a *.deb somewhere on the web, labeled "works for me".

So it should be a reasonable thing to give also negative feedback on the usability of the application. Which isn't always nice, but probably helpful.