the probability forum would be good for answering this i suppose.
JJ can often win unimproved but not against a lot of people, but don't adopt this mindset "AK, and JJ, TT, etc are drawing hands and could be ruined by a bad flop, so i don't raise preflop. i like to see the flop cheaply."
what you're up against is implicit collusion. preflop you have an edge against the 5 random hands, but you can't expect to win every hand when you have the advantage.
playing semi strong hands really depends on the game and your opponents though.

ok to sum up, i'd say a preflop raise with JJ is +EV because you also have good implied odds in those loose passive games. i wouldn't get into a raising war with JJ but i just think you're giving up too much by not raising it pf.