With regards to liquid water on comets, my thoughts conclude that although evidence is circumstantial in the terms of supposed solar system origins, liquid water as mud in comets interior will eventually be proven - most likely in the next couple of decades. The corollaries to this is that the only possible way to reconcile this to measured data is to include life in comets, stretch as a way that bilobate shapes are formed, and tectonic style surface movements to explain surface features.
1. There is no evidence for liquid water:
This is not strictly correct at all, as there is indirect evidence from many comet missions. Panspermia advocates are a group of scientists who note that the evidence is entirely consistent with there being liquid water in comets. There are no contradictions from Rosetta, and many otherwise unexplained surface features that have easy explanations if internal liquid water mud is hypothesised.
2. The connection between O2 and water rules out liquid water because liquid water cannot dissolve a level of O2 that high:
O2 was in fact considered impossibly unlikely until the Rosetta mission discovered it. Liquid water, molecular oxygen and life are all considered impossibly unlikely on small bodies, but all three are abundant on Earth and are connected to each other - ie. Life needs O2 and water - forms of life generate O2 and require water etc. An alternate explanation for both O2 and Water abundances is a pressurised interior, with abundant life which generates O2 among other respiration byproducts.
3. The temperatures and pressures both within and outside small body categorically rule out liquid water:
Clearly the surface is exposed to vacuum, which rules out surface liquid water. At hydrostatic equilibrium, the interior also cannot hold liquid water. However, if the interior was somehow sealed and able to hold at least .006 Atm pressure, and was, for whatever reason, warmer than the surface average temperature over its orbital cycle, then liquid water would be certain, given outgassing patterns.
4. Incredible claims require incredibly convincing evidence.
This is a common theme when alien life is posited as part of a narrative of what is happening. There are two possibilities - alien life is either 100% true or 100% false (in a comet in this case) If it is 100% true, then it isn't an incredible claim. Since we surmise the probability of life on a body based on the surmised possibility of liquid water, the argument that O2 is inconsistent its liquid water is a circular argument based on the assumption that alien life on a comet is impossible.
Ie. There is no liquid water because the O2 rules it out, there can be no life because there is no liquid water, therefore life cannot explain the O2.
So liquid water should not be ruled out until an actual internal measurement is made.
5. Comets are unchanged remnants from the early solar system. This rules out narratives where comets could evolve into what they are now.
All the factors that lean towards comets being pristine remnants (until the recent epoch of entering the inner solar system) can have other explanations, especially if life is part of the explanation. For instance, low density leans towards these not having been part of larger bodies. The activities of life within these bodies could have reduced the density (increased porosity) over time, meaning they could have been fragments of larger bodies (perhaps that had life as larger bodies)
