The sentence is making a comparison between science and other news agencies. The phrase "in principle" refers to the basic idea or concept, which is a better fit for comparing science to other agencies in terms of their role or function.
Option (A), principally, would imply that science is primarily or mostly like other news agencies, but it doesn’t convey the intended comparison of basic ideas or concepts.
Option (C), in principal, is incorrect as "principal" refers to something of primary importance, which is not the correct usage here.
Option (D), in spirit and form, although it might seem plausible, does not fit as well as "in principle," which directly refers to the fundamental idea or concept.
Thus, option (B) is the best choice.