1 Corinthians 10:30

For if I by grace be a partaker, why am I evil spoken of for that for which I give thanks? (KJV)

Then: A conscience beset Corinthian may continue to struggle with the philosophical issue by asking, "What can be wrong with my eating? I give thanks, enjoy the food, yet am condemned because I eat." (Based on the NLT translation used by Baker, p. 150). People often strike back at what doesn't seem fair. Paul here seems to be agreeing, "It's not fair, but is it right to be selfish about the kindgom of God?" Baker (p. 153) quotes Thiselton and Fee's reference to Psaml 24:1 which was reitereated in 10:26. The food has been blessed and is now purified. So what gives? The Corinthians had to figure it out and accept the logic, especially the underlying principle of "Love your neighbor," -- instance by instance, one person at a time. Paul could only present it, not force its acceptance.

Now: Discerning when personal actions affect the eternal salvation of another is as difficult today as then. Reliance on the Holy Spirt, one's conscience and the Word of God brings forth right decisions. Do the best you can and leave the rest to the Lord. Your heart is clean. If more is required, the Lord will let you know.

Extra source: Cornerstone Biblical Commentary 1 Corinthians (William Baker), 2 Corinthians (Ralph Martin & Carl Toney), ed. by Philip Comfort. Carol Stream: Tyndale House Publishers, c2006.