I'm brand new to the Arma franchise but I've got about a decade of PC gaming experience. Arma 3 isn't that difficult to pick up if, but it's definitely hard to master. I've watched all of Dslyecxi's introduction to Arma 3 videos and read his Arma 2 guide and that definitely helped me get the basics down - still have a lot to learn though. I believe attitude has a lot to do with how people play. I try to listen to my squadmates and what they're doing to help out as much as I can.
Griefing is a part of any game you play and by it's nature Arma 3 is very easy to do so. I haven't run into much of it, but there have been times when griefers will shoot fully loaded helicopters out of the sky and TK people in the field. Just goes with the territory of online gaming I guess.