I think you are mistaken here. Photons couple with charged particles due to their spin, this interaction can be seen through Compton scattering. https://en.m.w

I think you are mistaken here. Photons couple with charged particles due to their spin, this interaction can be seen through Compton scattering. https://en.m.wikipedia.org/wiki/Compton_scattering https://en.m.wikipedia.org/wiki/Compton_scattering However we have for example Neutrinos which are weakly interactive even more so than the photon and are not baryons (the real reason why neutrinos are not a baryonic DM candidate ;)). A neutrino will not interact with a photon at all since photons do not have an interaction through W and Z bosons (both W, Z and Photons are electroweeak gauge bosons) and neutrinos are not charged. There are a lot of reasons why you wouldn’t fall through the earth electromagnetism is just one of them, however even non charged baryonic matter can be “solid” and resist gravity for example neutrons will resist gravity through degeneracy it’s all a question of which type of interactions are possible. There is much more to particle interactions than charge. As far as photons interacting with neutrons, neutrons while being neutral in charge have a magnetic diepole which is why the photon can couple with them. You can make baryonic matter that is massive and does not interact well with photons, the LHC has been making some new baryonic matter but none of it is a good candidate for dark matter so far. But overall yes currently it looks like baryonic matter at least the one of the standard model without any extensions produces isn’t a good candidate for DM. :)