The most striking difference is that the Mindcrack community is far more mature than the Yogscast community. Every basket is going to have a couple of bad eggs but for the majority they are A-OK. I'd also wager the Mindcrack community would fit into the FTB world a great deal easier but that's an assumption more than anything.
This isn't to say every child or younger viewer of the Yogscast is loud and brassen as I know many are not but you don't need to dig too far to see a good example of what the general populous can be like.
Just please, for the love of all that is good in this world, do not let PewDiePie anywhere near this... Words cannot describe how much I loathe him and his fanboys.
I dont understand how it makes a difference if any of these people decide to play ftb, its either a single player game or a small server based game, either way you cant be effected by people you dont know deciding to play the same game as you.
Id also like to apolagise to anyone who read my last post as i usually stay out of threads such as this, i guess it just kind of annoyed me to see ftb's community actively wanting people to not play because they may have differing opinions to your own.
(This also sounds angrier than it should do so heres a doggy)