The verse before the one you show puts forth brother as law there
View attachment 122479
My brothers keeper, or law keeper, as love keeping the law would be being your brothers keeper in the sense of things
The principle in James 4:11 seems to follow: Mt 22:37-40
37 Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind.
38 This is the first and great commandment.
39 And the second is like unto it, Thou shalt love thy neighbour as thyself.
40 On these two commandments hang all the law and the prophets.
KJV especially verse 39. This, in turn, follows: Lev 19:18
18 Thou shalt not avenge, nor bear any grudge against the children of thy people, but thou shalt love thy neighbour as thyself: I am the Lord.
KJV
The intent, IMO, is: Since Ro 8:1-4
There is therefore now no condemnation to them which are in Christ Jesus, who walk not after the flesh, but after the Spirit.
2 For the law of the Spirit of life in Christ Jesus hath made me free from the law of sin and death.
3 For what the law could not do, in that it was weak through the flesh, God sending his own Son in the likeness of sinful flesh, and for sin, condemned sin in the flesh:
4 That the righteousness of the law might be fulfilled in us, who walk not after the flesh, but after the Spirit.
KJV;
therefore, judging one's brother contradicts the 'Law of the Spirit of Life'. which states that there is now NO CONDEMNATION.
At least that's how I see it.