I agree that Christians and postmodernists have used the notion of scientism as a cudgel against atheists and naturalists. But it doesn't follow that there's no there there at all, no real scientistic pattern. That's a kind of guilt by association argument.

Likewise, even if the term originated for religious purposes, that wouldn't imply there's no valid, helpful use of the term. That's the genetic fallacy. I'd just be careful to point out that arguments against scientism don't count at all against science.

I agree also that scientism isn't a "formalized philosophy," which was Jerry Coyne's point against the allegation. He'd say there's no consistency in the use of that label since the accusers would always define it differently.

That's why I say outright that scientism is just a prejudice, not a theory or a worldview. The prejudice can be expressed in different ways, just as any attitude or emotion can be.

As to the percentage of scientists and engineers that have this prejudice, I think it's strongest in the hard (math-heavy) sciences, especially physics. It's implicit also in the craving for scientific cache in disciplines such as economics and political science. And it's implicit in the burying of philosophical areas such as ethics, by charlatans in the self-help and happiness industries. The assumption is that the more scientific a discipline can seem, the more it's legitimized in the eyes of the public or the donors.

But I don't have data on the prejudice's prevalence. For me it's part of the academic culture war identified by CP Snow, and it's commonsensical to assume that power's going to corrupt you in that way. Science is more lucrative than the humanities because of its technological applications which can be more easily sold. The benefits of the humanities (civility, self-knowledge, virtue) are more intangible.

I think it's also telling how similar scientism is to racism: even as some folks insist they're not racist or scientistic (as the case may be), out pops the prejudice. A while back I showed this for Coyne, Sam Harris, and Neil deGrasse Tyson.

http://rantswithintheundeadgod.blogspot.com/2012/08/jerry-coyne-on-scientism-and-freewill.html

http://rantswithintheundeadgod.blogspot.com/2012/03/sam-harris-science-of-morality-case.html

http://rantswithintheundeadgod.blogspot.ca/2014/05/neil-degrasse-tysons-scientism-and.html