I keep running into the same argument over and over again: some beliefs or pieces of information are so obvious that it doesn't matter whether one has evidence for them. A similar line of reasoning is that if a belief or a piece of information has become public knowledge then it ought to be right; after all, it is so obvious that everyone knows it.
This line of reasoning is inherently flawed. Especially Muslims must be careful when they accept such 'public' pieces of information for the Quran says:
It is this commandment of Quran that led collectors of hadith to verify every person who narrated a saying of the Prophet (pbuh) even though a large number of concepts were public knowledge at that time. For instance, methods of prayer, zakat, fasting, pilgrimage were all well-known, but when hadith collectors collected narratives, they still ensured that the information was brought to them by trustworthy folks. In addition, they also verified the text of the narrative via textual analysis and related methodologies.
It should not be acceptable for a Muslim to take a piece of information, whether it be 'public knowledge' or otherwise, without verifying its sources. And the application of this principle should not be limited religious issues only since Quran's commandment does not make it specific to religion.
The need of the hour is to consider such matters with peace of mind and do the needful i.e. there is no harm in investigating non-Qur'anic knowledge including ahadith provided that the procedure has the virtue of honesty & modesty.