I don't consider it to be, but it certainly is for a large portion of the USAs population, mainly due to differing interpretations of what the word means, and the common perception (at least in small-town USA) of atheists being amoral as well.

It's kind of like "socialist" - many people think of it as inherently bad, instead of just a different set of relative values. I've lived in Sweden and can say that atheism, agnosticism, and socialism aren't bad, just different.

Exactly. It has a lot to do with the ambiguity of language, particularly english.

It is inflammatory. Not only to the religious but also to the very large percentage of people who see it as a strident position.

For something to be inflammatory it only needs to inflame.