I think bd is looked down, because it was an unintended and unwanted strat available in DotA, because the map didn't have any settings to prevent this (they later tried making the towers heal when someone bd's, but that hardly did anything in a late-game).
In LoL, if bd is seen to be a strat that drains too much of the fun from the game, then enough complaints should convince the mods to make changes that counter bd, like making the towers invincible if there isn't a creep in the vicinity, healing the tower, or increasing the tower's deadlines or something if there aren't creeps nearby. Until the mods start to try and prevent players from bd'ing, I think they intend for players to bd if there is a prosperous moment for it.
Personally, I don't like bd, because it one-sides the game to champions that bulk up and go straight to the towers which, without the general ethics of non-bd or inclusion of anti-bd measures, will change the game entirely to standing guard at your towers and sending out your own heroes to bd theirs. With free bd, the whole game will revolve around avoiding interaction and merely resort to attacking the towers your enemies aren't protecting.
As long as anti-bd DotA players continue to outnumber and actively resist strategic players, I think the game will avoid full realization of the superior advantage of bd.
I continue to bd when possible, because of its advantages to win. The mods' non-reaction to bd will continue to tell me they want us to bd. People chew me out sometimes when I bd and I just tell them to complain to the mods so they can find out how wrong they are, by the non-response they get. If the mods ever respond to their complaints by fixing the issue I'll still be happy, because the game will be changed to my perspective of a more fun way to play.