It would probably behoove most partisans to presume that if someone is in their audience, especially if radical, the audience doesnt have any backdoor access to the ingroup from where they came, chameleon armor to blend in seamlessly with ingroup despite turncoating, and then work some magic to turn a larger ingroup tide against itself to stop everyone else from drowning in it.
There are just too many static presumptions that dont account for the dynamic process of rebuking status quo systems and ideology to keep thinking 'and then Carl will talk to two people and woo one, those two will do similar and pass it along, so on and so forth, then change' is actually how any of this shakes out.