As a mother whose 12-year-old just spent $50 of his birthday money on loot boxes in Overwatch, having some idea of the odds of his getting the skin of his dreams would definitely have given me a better argument to dissuade him from doing this. Letting people - usually kids - know the odds would bring into focus the idea that this is gambling, and spark conversations in families that may be less aware.
I do think that this kind of gambling is insidious for youth. For this reason, regulation should be considered (just as it is for marketing alcohol to children). I have not considered what the best form of regulation would be. Offhand, I think it would be important to state the odds of winning on the same page where loot boxes are purchased, not just when the game is downloaded, for example.