I'm just telling you what I see in verses.
Does Jesus telling us He won't force a man to leave mean he can't leave? The answer seems self-evident.
Jn 6 gives account of many disciples turning back and no longer walking with Jesus after hearing Jesus teach at the synagogue in Capernaum about His blood and His flesh, the Bread of Life. They said, "This is a difficult teaching (declarative statement). Who can accept it (rhetorical question)?" And Jesus answers with His own rhetorical question, being aware of their grumbling, "Does this offend you?" (Jn 6:60-61). And then my summary of Jesus' reiteration of the Father's will for those that believe and those that do not (Jn 6:64-65).
And Jn 6:66 shows those that "turned back and no longer walked with Him." I'm confident the deduction can be made that these heard Him 'in the flesh' which profits nothing.
Verse 67, "Then Jesus asked the twelve, "Do you want to leave too?"
and
Verse 68, "Simon Peter replied, "Lord, to whom would we go? You have the words of eternal life." And it can be deducted that Peter heard "the words I have spoken to you are spirit of they are life."
And (my summary of Jesus' reply), 'This is exactly why I chose you, except, of course, for the one who doesn't believe.'
So, yes, technically, they weren't captives of Jesus and were free to go, but why would they if they believed Him in spirit and in truth?
And, after the event of Peter's denial? Why did Jesus (have to) direct the others, "Go and fetch Peter." Was it because Jesus was fully aware that Peter had no intention of coming on His own? The others would've retrieved Peter saying something like, "The Master has bid you to come with us, that you should return to Him." Imo, Peter must've had to muster up quite a bit of faith in order to return to Jesus, and perhaps Jesus call for him offered Him at least a mustard grains' measure to start out with. I can only imagine the inner conflict Peter must've been going through in returning to see Jesus again. And the ultimate comfort he received at the third time Jesus led him to say, "You know all things... You know I love you."
But Peter was hurt that Jesus asked him a third time. Might he have been hurt because he harbored the thought for even a second that Jesus didn't believe him? Personally, I think Jesus' intention in that was to work that doubt, that fear which Peter had previously demonstrated three times, out of him.
Then, Jesus told Peter what would happen to him. And what harder saying could Peter have heard other than that?
So,