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I've seen some treatments in the scientific popular press (podcasts) that consider the possibility that dark matter can be explained by an error (or new term) in our understanding of gravitation & mechanics. I don't see anyone (in the podcasts) considering whether our understanding of "emission" or blackbody radiation were complete. Why are scientists more willing to consider new laws of mechanics than consider we don't know everything about how "regular matter" reacts with or emits photons. I'll admit that some of my "gut feel" is in a guttural reaction in college to the implausibility of a T to the fourth power in Stefan–Boltzmann law.

If the full answer where to be found in this P.SE question, I'll study it in greater detail.

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This is a research topic with lots of assumptions, especially on CMB and cosmology part. Which emission do you mean the one we observe now or the one which contributed to microwave background? –  Asphir Dom Jul 15 '13 at 22:53
I apologize I am an ignorant layman, only engineering-level training in semiconductor physics. I mean "why we think it's dark" –  pterandon Jul 15 '13 at 23:06
It's "dark" because (a) it is non-luminous and (b) because we do not really know much about it. –  Kyle Kanos Jul 15 '13 at 23:21
Absolutely no need to apologize, it is a valid question. Shortly - emitting and absorbing properties of matter(atoms) are well studied in spectra of distant stars, their properties are more or less same as in lab on earth. Dark matter claim is based not on visible light astronomy observations but on interpretation of microwave background. Your idea is also a possible scenario -- people are looking even for variations of fundamental constants in distant star systems, again using star spectra. –  Asphir Dom Jul 15 '13 at 23:23
The emitting properties are considered in hot things (stars) and room temperature things (labs), but what about really, really cold things? (Again, I'm stuck on the philosophical implausibility of a T^4 equation.) And to get more mundane, suppose I put my finger in front of my eye-- is my finger now responsible for telling me about all the matter it occludes? Thanks! –  pterandon Jul 16 '13 at 0:57
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The point about black body radiation is that we don't need to know the precise mechanism to predict its properties. There is an excellent description of this in Luboš Motl's answer to What are the various physical mechanisms for energy transfer to the photon during blackbody emission?.

On the other hand, while MOND and its various extensions may give reasonable fits to observations there is no obvious mechanism to explain why GR would be modified and what causes it. By contrast there are many possible mechanisms for producing weakly interacting particles of the type required for dark matter. In fact if supersymmetry is realised in nature dark matter seems an almost inevitable consequence. It makes sense to study the mechanisms we have some grasp of before jumping into mechanisms we have no theoretical support for.

It seems to me that you start your question with an invalid premise. As far as I know no-one doubts the basic principles of black body radiation. The precise nature of the interactions may be in doubt (though not as far as I know - do you have a reference?) but as Luboš explains that wouldn't affect the general properties. On the other hand there are excellent reasons why dark matter is the subject of massive and continued speculation.

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