Some will mistake scientism for science because scientism masquerades as science. But please do not confuse science and scientism; their methods and objectives are completely different. Also, I need to say that science and Christianity are not at odds with one another, what-so-ever.
In my undergraduate studies in behavioral science (at the University of Utah), I engaged in a number of classes focused on research design. These classes emphasized scientific principles and even the scientific method. I also took a number of natural science courses that re-enforced the same principles.
This is science. The first step of the scientific method is to ask a question, typically based on some kind of observation. This question should be structured in some way as to take a measurement and correctly gather data. At the point of simply asking the question, it should be free of any definitive answers, at least at any point before the research is concluded. An open mind is necessary. Next one should survey the body of knowledge to gain an idea of what work has been done to answer the question. From here, a testable hypothesis should be formed. The objective from this point forward is to prove or disprove the hypothesis. In order to accomplish this, testing with experiments must be employed. This can be laboratory work or organized methods to arrange data in a useful way, or even some other way to test a hypothesis. Sometimes it is only a matter of collecting data and running it through a statistical formula. Other times elaborate and lengthy tests must be conduced. Once complete, the data must be analyzed. It is here that answers are forming (and not until this step). Then the answers are to be reported.
Scientific practice often requires that the testing is repeatable. Also, academic scientists are highly encouraged to use language that suggests they do not hold definitive answers. As more and more testing and reporting provides more and more evidence, people will tend to lean in the direction of the evidence. There is hardly ever a "smoking gun" or "absolute" proofs. Instead, as more and more research is completed the evidence becomes more and more compelling. In addition, unsuccessful attempts to disprove the reports will also lend credibility to the answers.
Scientism on the other hand starts with an answer. It then uses a mutant science to develop the question in order to get back to the desired answer. Plus, you will often find that scientism reports definitive answers and demands total proof of positions in which they do not agree. For example, a worshiper of scientism will demand complete and total proof that God exists but they themselves cannot prove by the same standard that God does not exists. This is because the approach is flawed. We should be weighing evidence. Scientism does not however, because it has already started with a position that God does not exist.
Take this article by Stephen Hawking for example: "Why God did not create the universe." You might notice the lack of cautious scientific language. You may also see that Hawking makes amazing observations, that when weighed against other evidence, such at the Bible, or other people's personal observation could suggest a creator. A scientist should remain open to all options until disproved. However, lines like "Spontaneous creation is the reason there is something rather than nothing, why the universe exists, why we exist. It is not necessary to invoke God to light the blue touch paper and set the universe going" suggest a predetermined objective and lack of academic caution. It is perfectly okay that he makes these claims; however, it is not okay that he masks them behind science. (He would be better off making claims such as this one in the realm of philosophy.) And this is where I run into problems with sceintism.
*Photo of a young Stephen Hawking provided by NASA and is in the public domain.