Peter did not sin, for he was operating on lesser belief than Paul in relation to circumcision.
Peter was sinning because he was not doing what the Holy Spirit was filling him to do. He was sinning against how the Holy Spirit would fill and guide him. And Paul says he acted out of fear >
"There is no fear in love; but perfect love casts out fear, because fear involves torment. But he who fears has not been made perfect in love." (1 John 4:18)
So, Peter was sinning against how God would have him love.
And Peter did know God had received Cornelius and the others, just as the Jews.
And Paul says it was
"hypocrisy" and that
"even" Barnabas went along with it. Hypocrisy is one of the sins which Jesus was more angry about, than a number of other sins. So, it is clear enough that Paul means they were wrong. Again > this is in Galatians 2:11-13.
So, in order to justify a false idea about sinless perfection, one has to deny that certain sins are sin.
Also, we have how John was
"in the Spirit on the Lord's Day" (Revelation 1:10) and receiving the vision of Revelation, but he fell down to worship an angel. I will offer that John a major leader in Jesus Christ's church full well knew he was not supposed to worship angels. But even while he was so blessed, he still could sin, but he got closer correction since he was so close to our Father.
But, one time when I brought this up, a person simply denied that it was a sin to worship an angel . . . even though the angel clearly told John not to do that.
Revelation 19:9-10. Revelation 22:8-9.
I think it is clear enough that he did not do this only once. He was even told not to, but did it again. And the Holy Spirit has him tell us so we can learn from his error; because John is an example of honesty, instead of just denying it was wrong.
It is good to have leaders who are
"examples" (1 Peter 5:3) by telling us however they are or can be wrong. Then we can learn how we need correction, and we can pray for them along with us all to get the correction we still need > James 5:16.
So, yes people will throw out what means getting real correction, of our nature . . . not only outwardly reforming ourselves and making a show.
I have been able to do things, as a gesture to my own self so I can suppose I am the way God wants. But self-produced change is not the same as how God's love effects our nature