I am at a lose to work out why so many are upset about this visit. FD have invited groups before, and no doubt they will do it again in the future. So what that they invited a bunch of talking heads from YouTube, they had to select a group from somewhere, maybe next time they will select a bunch of posters from here, who knows and who cares!
And the visit won't change the outlook of the invitees either, whether they are White Knights or toxic Doom and Gloomers, what they say on their channels won't change because they have a fair idea what their subscribers want to hear. Lets say one of the invitees is ultra toxic, always finding fault in everything FD does. If they suddenly start sprouted how magnificent FD is, their subscribers will drop as a result. Likewise if someone was never critical of FD but suddenly started to rant and rave about the company, they would lose subscribers faster than a newbie can lose their first Anaconda.
The invitees won't be releasing a 'tell all' clip because they would have signed an NDA, they may hint that 'big things are coming' but are hopefully smart enough to know the consequences of breaking the NDA.