Science seeks to _explain_ the generative mechanism(s) of X. Debates within the philosophy of science concerns exactly _how_ science has done so or should do so. For an explanation of the generative mechanism(s) of X to be true, the said generative mechanism(s) must be real and transfactually efficacious; otherwise an explanation is not true. Explanation is not at all the same as prediction; however, under certain circumstances (where we can produce a closed context), a correct explanation of the generative mechanism(s) of X allows us to produce the X in question, and, under other circumstances (where it is not possible to create a closed context), we can at least predict where X is, how X will act, etc. with reasonable accuracy. If science doesn't work at all, human beings wouldn't have come to exist in a society that depends upon mass industrial production of necessities, for instance.
Ideology, on the other hand, presents (an imaginary solution for) an imaginary explanation of an actual (or imaginary, as the case may be) phenomenon, problem, question. For instance, for the religious, Providence serves as an imaginary explanation of many things (e.g. poverty, evolution, gender inequality, etc.). For many apologists of capitalism, 'merit' or lack thereof explains the class relation (if admitted at all) or more generally 'stratification.' Both are not only untrue but also reactionary, and we must combat them in a Gramscian war of points.
Criticisms of ideology are important especially in the disciplines that directly concern the explanations of the social world -- exactly the disciplines to some of which Foucault (a very perceptive man) paid the most attention. Why? It is evident that in the social world, effects (e.g. ideological explanations of poverty that blame the victims) become material forces or causes for the reproduction of the class society of which they are effects, in a vicious circle. We are interested in breaking this vicious circle, aren't we?
>> Science can, however, contain unscientific ideological elements
>> but it is despite them that it is science. Science in class societies
>> is suscptible to ideological distortions of various kinds
>> (i.e. social Darwinism, "scientific" racism, sociological theories
>> of "cultural deprivation" and the like) but from that fact it
>> does not follow that science itself is inherently ideological.
>
>there's no such thing as 'science in a classless society,' so
>science is by definition 'subject to ideological distortions.'
>small wonder that someone should read what you say as somehow
>akin to theology.
The good (or bad) of any human endeavor cannot be correctly evaluated from the point of view that doesn't posit a future without classes (and keep in mind that this future is not guaranteed in a Hegelian fashion -- it is what we can but may very well fail to create). All truly scientific endeavors contain the kernel of truth beyond ideology when seen from the point of view that posits a future classless society (e.g. biology and medicine have been distorted ideologically; nevertheless, true explanations that have been discovered in these disciplines will serve, minus capitalism, sexism, etc., to enhance human happiness, for instance, by relieving pain).
For the same reason, I'll never 'bash' art, literature, etc. _in general_, even when particular instances of them can be so terrible as to drive many people to despair. In a future of classless society, for instance, literature and interpretations of it can provide countless hours of pleasure, and they will be, in my view, an indispensable good that will add greatly to the conditions of individual & collective human flourishing that communists seek to create.
Therefore, those of us who have not given up on Marxism or an adventure to create a classless society cannot do without the concept of ideology (that stands in opposition to truth). On the other hand, for those post-Marxists who have abondoned this objective (such as Foucault), it makes a lot of sense to say that science can never be distinguished from ideology. In this sense, postmodernism is an ideological expression of the despair of leftist intellectuals. 'No Future,' they sometimes shout in a futile protest. At other times, postmodernism helps them to reconcile themselves to a 'world without a communist future.'
Yoshie