Christ gave up his life for that person. Wouldn’t you at least be willing to give up going to dinner for him—because, as you say, it doesn’t really make any difference? 1 Corinthians 8:11 (TM)
Eating meat sacrificed to idols is not a huge issue among Christians today like it was for the believers in Corinth. Nevertheless, the principle applies to any number of activities upon which Christians have various opinions. I remember, when I was a teenager, I listened to a Christian scholar talking about gambling. I had always assumed that gambling was among the top ten sins along with "smoke, drink, chew and going out with girls who do." I was surprised to hear this respected scholar lay out a Biblical argument that gambling, while foolish, is not specifically a sin.
Drinking, dancing, clapping in worship, working on the sabbath, and listening to rock music are other activities upon which I’ve heard a wide range of opinions among believers. The debate surrounding some subjects can turn heated and ugly. That’s when Paul’s discussion of food sacrificed to idols becomes an important guide. Our admonishon is to be kind, loving and gracious with one another. Those who take a permissive stance on such matters need to be considerate and show deference when you’re around believers who feel differently – not flaunting your freedom and aggravating the situation.
It all comes back to putting others ahead of yourself.