I don't even think that was rude, but there's a much stronger argument here.
There doesn't always need to be a compromise position... http://xkcd.com/690/
There are definitely two points of view, though I'm not sure there are enough people espousing each to call them both 'camps'...
That last sentence was snarky.
Not to mention, completely unwarranted.
Of people expressing an opinion (up to this post of yours), I count 7 in the "nothing wrong with ducking out" camp, and 4 in the "it's polite to ask" camp, plus one ambiguous. 4 is smaller than 7... but not
so small that it doesn't even register. More to the point,
7 is small too: the sampling error with single-digit integers is huge. Drawing strong conclusions is statistically unsound.
But let's not get sidetracked by technicalities.
The larger point is that I learned something about the culture of the Isotropic community. Judging from this thread, it seems a significant fraction (probably a majority) think there's nothing wrong at all with leaving at any time, for any reason. Some of them have taken the time to explain their views. While I don't agree, I'm now much less likely to hold it against someone who ditches the game before I can play my engine.
On the other side, it's hard to deny that lots of other people get annoyed when the game ends prematurely. You don't have to ask permission or anything... but if you at least say something before you leave, you make Isotropic a more pleasant place.