Minecraft, and other games, can be very good for teaching. What blows my mind is how schools react to it. The anti-gun nuts have pushed schools so far that some of them won't allow anything Minecraft. Why?
A quote from our local ART teacher - 'a pickaxe is a weapon.'
I guess as an art teacher she has never seen a statue.
Minecraft is about building, and having fun doing so. Girls will frequently play just creative, preferring to not deal with the violence of creepers and other monsters. Girls tend to have fun just making things, as typically females tend more towards creativity.
Boys play creative too, but are more likely to enjoy the monsters. For those who aren't aware of this creepers aren't people! (OK, ok, everyone on this group is aware, but I swear there are some dumb people out there who aren't.) While boys certainly enjoy making things, they also tend to enjoy action based games and thus may want to deal with monsters.
Mojang made a game that allows both boys and girls to have fun, doing whatever they want to do. It has been a teaching tool from the beginning. Kids learn how to use logic from the minute they start the game (especially after it turns dark!) As parents our job is to talk to our kids and help them understand right from wrong. You can't do that in a bubble. Minecraft and other games have a lot of positive aspects, the negatives (if you perceive any) can easily be used to teach as well.