“One person has faith that he may eat all things, but he who is weak eats vegetables only. The one who eats is not to regard with contempt the one who does not eat, and the one who does not eat is not to judge the one who eats, for God has accepted him.” Romans 14:2-3 (NASB)
When it comes to judging brother and sister believers regarding “right and wrong” activities, we realize that “back then” in the 1st century it was not so different. One example was food—especially meat. Was it acceptable to eat meat offered to idols? The stronger believer, whose mature faith allowed him to exercise his freedom in Christ by eating the inexpensive meat sold at the pagan meat markets—inexpensive because it may have first been sacrificed to a pagan deity. On the other hand weaker Jewish and Gentile believers abstained and ate vegetables only. They believed the meat was unclean*. Some believers today still declare some activities “unchristian” and called it sinful to participate. These may be activities for which God has not prohibited but the affiliations may offend some. The strong hold the weak in contempt as legalistic and self-righteous do-gooders; the weak judge the strong as irresponsible or even depraved. But God has given us a promise that His acceptance is not based on observing such rules and legalism but on His love and grace. Let each live and love our brothers and sisters while accepting all as living according to their own conscience before God.
*This is different than reasons why vegans abstain from consuming animal products today.