Firstly of course I would because it's true.
Secondly this is what you said 'Do you deny that hundreds of people have been added to Facebook groups about the case, sometimes without their knowledge?.' So how many do you think have been added to Facebook groups 'without their knowledge' Alfie.
As to your third point when a friend adds you to a Facebook group you are informed and can leave if you wish.
Firstly, truth is subjective - in my opinion what you say is not true.
Secondly, I don't have a specific number because I'm not quite sad enough to log numbers of disgruntled FB "sceptic" site add-ees. I've seen several people complain about being added, put it that way. You will of course choose to disbelieve me, that's fine - it's your choice.
Thirdly - yes, people can leave if they wish but that is beside the point, which was that there is a recruitment drive in operation to increase forum and facebook numbers. That is why links to both are frequently tweeted too.