CAPWARD
Thing is, situation reversed, would you trust it.
He wasn't exactly a HYDRA flunky. He might not have been involved at the Triskelion but we knew, we both knew what was happening and what the end goal was. He believed in it about as much as I did, but it was useful.
You want him to trust that you won't just shoot him? Or if not you than Barnes, who has every reason to kill any member of HYDRA he sees.