Why was Paul accused of not bringing the truth?
Paul was accused of not bringing the truth because he refused to align with the Judaizers in Jerusalem, was no longer working hand in glove with Peter and the eleven, and proclaimed a message they did not know. Those false accusations should have been aimed at false teachers.
Les explains that Paul was accused in verse 17 because he was not agreeing with the Judaizers in Jerusalem and was not working hand in glove with Peter and the eleven anymore. Paul was out proclaiming something they really knew nothing of, so he was bombarded with false accusations that should have been reserved for false teachers. Les notes it is often the other way around: instead of false teachers being bombarded, those with the truth come under attack.
When I therefore was thus minded, did I use lightness? or the things that I purpose, do I purpose according to the flesh, that with me there should be yea yea, and nay nay?