This is a strange interpretation of how theories and generally science works in practice. If the aforementioned poster is doing their best to discredit an existing theory the information from that is implicitly involved in any subsequent theory with greater explanatory power or predictive ability.

It was known a bit after Newton's theories and prior to Einstein's Relativity that Newtonian Mechanics could not account for the perihelion precession of mercury. These serve as baselines for new theories to predict or explain. Popperian Falsification is one school of thought in philosophy of science more or less predicated on the idea you cannot ever prove a theory, only disprove them. An important criteria then is to allow for testable hypothesis with clear fail states. There have been other developments and more fruitful ways of looking at how science works in practice but if we stick with this then no theory can be proven, we only work with whatever theory is most amenable according to some criteria.

Theories already exist, it's inevitable that they will be used to explain phenomena, someone engaged in introducing auxiliary hypotheses and theories to explain away or contend with the core of their theory is not 'doing the opposite'. Rather it might be useful to think that a lack of evidence of something means it is not worthy of consideration among the litany of hypotheses, only certain evidence of something not occurring would be good enough to completely abandon a hypothesis. As that is significantly more difficult and the extent of evidence required great, one can avoid all this by accepting that all theories are wrong and some are seemingly wronger than others and it isn't necessary to completely abandon them. Instead they can be kept in a provisional space with other theories which are less productive or fruitful until they may be called upon.