How'd you even come across such an FC? Generally the unspoken rule is Don't join an FC if it's a random invite.

As mentioned each FC has their own 'culture' so you've just stepped on a bad one. Same experience with my first FC. Then again, I didn't really have much insight as to what an FC was.

Best advice is leave the FC, no point in feeling guilty about it. Advertise on here for a sociable FC or on the Party Finder. Assuming you've completed the quest for Sastasha.