Peter,
There was NO assumption that dark matter cannot interact - that was established by the evidence - the location of the identified lens effects relative to the point of collision and the non-interacting galaxies (I'm specifically referring to the Bullet Cluster here). Again, this is not just my interpretation but, as best I can determine, the consensus interpretation of the astrophysics community. Whatever produced the lens effects could not have physically interacted with any other material during the collision.
The disperse x-ray emitting gas from the two galaxies did interact, that is why they remain near the point of collision - unlike the non-interacting galaxies and whatever produced the lensing effects.
I asked one thing of you - to explain how disperse ionized gas or plasma particles could have proceeded far beyond the point of collision, as did the galaxies. You have not complied. Instead you dismiss the compelling visual evidence that the lensing source (including the clusters' galaxies) did not interact during the collision.
That the lens effects remain coincident to the galaxies following collision indicates that the galaxies almost certainly contribute to the identified weak gravitational lens effects. No dark matter would be necessary if there were some systematic error in the estimation of collective galactic mass, but I am not capable of identifying any such error, so I cannot make that claim. The alternative is that weakly interactive massive particles are present contributing to the lensing effect also produced by the clusters' galaxies.
There is no need to complicate this analysis - as established by consensus, the location of the lens separate from any gaseous matter is clear evidence that the identified weak gravitational lensing effects could not have been produced by any disperse gaseous material, including molecular gas, atomic gas, nucleons or electrons, since disperse particles within the two colliding galaxy clusters would have interacted as did the x-ray emitting gas.
The onus is on you to disprove the consensus interpretation that the separation of lensing effects from gaseous galaxy cluster intracluster media precludes their contributing to the identified weak gravitational lensing effects.
Jim