@ Arthur Eld

Whole books have been written about how to define ideology. Arguing that sth. can (or cannot) be classified as ideological depends on your definition of the term.

The term is used by some in a neutral sense for systems of ideas in general, especially in the social sciences.

For others, in the tradition of Marx, ideologies are "the systematic, limited, perverse thinking of opponents he saw as intellectual tools of corrupt regimes" (http://www.semioticon.com/seo/I/ideology.html).

I guess the people you argued with about atheism used ideology in this sense: as a derogative term implying the system of ideas in question is false. Like you wrote: As a swear word.

Some social scientists think that the first definition is way too broad and thus renders the term irrelevant as an analytical term. The second definition, on the other hand, easily leads one to think that it is always the other worldview that is an ideology.

Some social scientists, like Klaus Arnold (a communication scientist) use the term ideology to refer to (all-encompassing) interpretations of the world which supposedly are true in an absolute sense and which are not open to critical examination and change. Thus, they are preserving the Marxian notion that ideologies are sth. problematic and sth. to be criticized. But they also give us a list of characteristics for deciding whether a certain system of ideas should be called an ideology or not.

I normally use ideology in the third sense. According to this definition of ideology, most religious world views are ideologies, while atheism (as normally defined), clearly is not an ideology.