If your brother or sister is distressed because of what you eat, you are no longer acting in love. Do not by your eating destroy someone for whom Christ died. Therefore do not let what you know is good be spoken of as evil. For the kingdom of God is not a matter of eating and drinking, but of righteousness, peace and joy in the Holy Spirit, because anyone who serves Christ in this way is pleasing to God and receives human approval. Romans 14:15-18
As Paul ends this passage on grace, he is specific in his application of the principle (eating and drinking rightly) but it applies to most other situations. Unity in the Body of Christ is important and should be important. His overarching argument seems to be something like this: there are big things and little things to be concerned about in the church. Concentrate on the big things. We tend to not know the difference. Or perhaps we like to think the small things are big things, and in our minds, maybe they are. There are relatively simple questions you can ask that might help you determine whether the topic is big or little.
What will this topic look like to the church in 100 years? Will it seem petty and insignificant to them?
What did other generations of church goers think about the subject? A quick Google search could tell you all you need to know.
Lastly, what would non church goers think of the topic if they heard about it? Whether we know it or not, these people are watching us, how we act, how we interact with us and with those around us. They are looking for truth. Will they find it in the big and little things we surround ourselves with?