The Christian who talks down fellow believers sins

Do not speak against one another, brethren. He who speaks against a brother or judges his brother, speaks against the law and judges the law; but if you judge the law, you are not a doer of the law but a judge of it.  There is only one Lawgiver and Judge, the One who is able to save and to destroy; but who are you who judge your neighbor?
-James 4:11-12

The Christian who talks down his brother sins.  'Speaking against' carries the idea of talking down someone.  Some translations have 'slander' or 'speak evil' here.  Derogatorily or denigration also captures the idea.  James is saying that 'trash talking' the brethren is out of bounds.  "Disparaging remarks about someone, which can include false statements." (Biblehub)

Does this include false and true statements?  Yes, while the definition of slander is false statements; a person can speak out against another believer maliciously, in a 'speaking down' fashion, where they arrogantly assume superiority. in an unloving fashion.  A person might believe they have very damaging truth about a brother that is really (wild) speculation, or they may believe something about a brother that is based on their personal experience with that person that was negative.  But, when we perceive that we have had a bad experience with someone, that other person may have a very different perspective!

We are always evaluating and forming opinions.  But speaking out about other Christian's shortcomings, sins, failures, or faux-paus is wrong.  We are called to love, being doers of the law. But when we publicly shame and ridicule or mock other believers, we are audaciously taking God's role and actually saying "I am playing the role of judge, jury and executioner".