There's 3 big downsides to plain packaging that you have conveniently brushed past.
1) That it is not evidence based. Much like the alcopop tax the industry experts were all involved with big-pharmaceuticals who market smokeless nicotine and people directly employed in quitting related professions who have ulterior motives.
2) That it harms tourism - (1. Many asian markets that have 50%+ (majority) male smokers (China, Japan, Koreas, Russia) think it is disrespectful to treat adults in such a fashion. (Won't quit for health benefits, but will for basic packaging?). Also it makes it alot harder for poor-intermediate level smokers to identify a cigarette that is the same strength as what they smoke (heavy cigarettes make you sick, light leave you unsatisfied - there will be no way to choose now when you are unfamiliar with local cigarettes).
3) It hurts domestic retail trade. I used to sell cigarettes at a petrol station. Half of all revenue from non-petrol sales came from tobacco. Considering there were 100+ tobacco products at this store, I have no idea how I could pick the right pack and finalise the transaction in the 30second or less window that I usually did - in fact such a move will involve searching longer then an average transaction. Additionally stores that offer tobacco for sale will not be readily available - an additional hazard for tourism when alot of our market are big smokers.