Summary: "Everyone knows" can become an excuse for our bias in the church. The Apostle instructs us to see our strength as imposing responsibility rather than conferring privilege.
“Concerning food offered to idols: we know that ‘all of us possess knowledge.’ This ‘knowledge’ puffs up, but love builds up. If anyone imagines that he knows something, he does not yet know as he ought to know. But if anyone loves God, he is known by God.
“Therefore, as to the eating of food offered to idols, we know that ‘an idol has no real existence,’ and that ‘there is no God but one.’ For although there may be so-called gods in heaven or on earth—as indeed there are many ‘gods’ and many ‘lords’— yet for us there is one God, the Father, from whom are all things and for whom we exist, and one Lord, Jesus Christ, through whom are all things and through whom we exist.
“However, not all possess this knowledge. But some, through former association with idols, eat food as really offered to an idol, and their conscience, being weak, is defiled. Food will not commend us to God. We are no worse off if we do not eat, and no better off if we do.” 
“Everyone knows…” No doubt we have each heard this phrase used—perhaps we’ve even used it ourselves. Usually, the phrase is employed to mask a deficit of knowledge. “Everyone knows” sounds as if it is an appeal to common knowledge; however, momentary reflection will demonstrate that common knowledge is often anything but common, let alone knowledge. In many instances, common knowledge cannot even qualify as knowledge—it is more akin to bias, prejudice, unfairness! Common knowledge almost always is built on supposition that may have only a tenuous relationship to knowledge. The appeal to common knowledge often reflects social bias rather than encouraging rigorous thinking. The concept of “crowd sourcing” can become a means of ensuring that we achieve the lowest common denominator rather than reaching for excellence in our reasoning.
Many people are not aware that the appeal to “common knowledge” as an argumentative device is not an invention of the contemporary western world—it has ancient roots. While I suspect that a minimum of research would allow us to demonstrate such linguistic devices are found in almost every culture throughout the ages, it is assuredly the case that among the earliest churches people appealed to common knowledge as a means of disarming those with whom they were arguing. “Everyone knows” was apparently bandied in the first bloom of the Faith.
In the Church of God in Corinth, a saying appears to have been commonly employed to cut off argument. That phrase was “All of us possess knowledge.” Today, we would say, “Everyone knows…” It was a phrase that would be employed whenever someone wanted to end the argument. After all, who can argue against the majority? We who call ourselves by the Name of Christ today, need to hear again the words of the Living God: “You must not follow a crowd in wrongdoing. Do not … go along with a crowd to pervert justice” [EXODUS 23:2 CSB]. When everyone agrees, make certain the agreement aligns with the truth!
WE KNOW THAT “WE ALL HAVE KNOWLEDGE.” “Concerning food offered to idols: we know that ‘all of us possess knowledge.’ This ‘knowledge’ puffs up, but love builds up. If anyone imagines that he knows something, he does not yet know as he ought to know. But if anyone loves God, he is known by God” [1 CORINTHIANS 8:1-3].