Defect

"Defect" used this way is not like "betray" although some people may consider a defection to be a betrayal. It can have a positive or negative connotation depending on which side of it you are on. If a French agent "defects" to ISIL (just to grab a recent headline), I expect the French to see that as a negative and ISIL to see that as positive.

It depends on the author of the report.
If I witnessed refugees fleeing to an alternate country - I would report it as such - "Fleeing, flee, fled"
How you paint a picture directs the observer.
To 'defect' implies switching loyalties.

I feel that the word does have a negative connotation simply because of the negative definitional words like "abandonment" and "disowning."

Thanks for the answers , I think that the word has both positive and negative meaning.