“Howbeit there is not in every man that knowledge: for some with conscience of the idol unto this hour eat it as a thing offered unto an idol; and their conscience being weak is defiled.”
King James Version (KJV)
8:7 Some eat, with consciousness of the idol - That is, fancying it is something, and that it makes the meat unlawful to be eaten. And their conscience, being weak - Not rightly informed. Is defiled - contracts guilt by doing it.
1Co 8:7 [There is] not in every man that knowledge. While "we", the better informed, know better, still there were some in the church who had not entirely outgrown their former superstitions. They could not realize that an "idol was nothing" (1Co 8:4). Their conscience being weak is defiled. Meat that came from idol sacrifice was to them the meat of the idol. They could not eat it without their conscience being "defiled".