1. That all these theories are the result of an error. For example, an erroneous initial assumption that Type 1A Supernovae can be used as "standard candles". Maybe they can't. In which case the whole cosmological distance ladder is wrong, the expanding universe is an illusion, an artifact resulting from incorrect distances being assigned to galaxies with red-shifted light. Maybe the red-shifted light itself is an instrument error of some sort.

2. That space-time is riddled with permanent gravity wells, like galaxy-sized dimples, regardless of the presence of matter. Galaxies and galaxy clusters just slosh around inside them, giving the appearance of more mass than can be seen. Maybe these dimples result from an interference pattern of gravity waves of unknown origin.

3. That there is no mystery, but researchers depend on grants to get published, and certain research topics are more popular than others, and therefore tend to get more funding.