And on top of all the other reasons people have given for finding the illegal drugs/alcohol pictures less displeasing, there’s the matter of humor.  
Absurdity is one of the fundamental elements of humor. The cast being all-out stone-dead alcoholics or druggies is, statistically, less unabsurd than them smoking cigarettes, which makes it more humorous. It also distances it from real life experience (even if you know a lot of marijuana smokers, you probably still know more tobacco smokers), making it less “close to home” to something which most people find ubiquitious, unpleasant, and entirely unnecessary (for values of necessity which include an arbitrarily high quality of recreation).

Nah flutters blazes it

@PwnyPony  
I can understand the second-hand smoke. I don’t like smokers either, and I suspect these big tobacco companies trying to push politicians to uphold the anti-weed and cocaine laws. Maybe that is why you guys hate it. Alcohol is purely self-inflicting, in terms of physical health.

@Background Pony #0EFE  
I… don’t think smoke can expand your lungs.

@Deserter  
There’s more tar in marijuana smoke, so technically it’s “worse” for you on equal grounds, but there’s this: If you smoked the same amount of weed per day as a tobacco smoker smokes tobacco, you’d be broke and burned out fast. Also, tobacco smoke constricts the lungs while marijuana smoke expands them.

@PwnyPony  
I still don’t understand how smoking pot won’t fuck up your lungs.

@SeraphimDawn  
It really depends on the drug when it comes to drugs. I support legal weed but am against heroin, crack and any other physical harming drug.
 
Smoke is easily passed to those nearby drinking is not going to affect those around you unless you can’t handle your drink.
 
Smoking and weed. Weed being the less harmful of the two (assuming you are smoking the weed not space caking) to be passed on.
 
My dad was a smoker and all the white plastics in the house turned a yellow creamy colour and dust was very thick in my computers fans.  
He eventually quit but his lungs were damaged and eating gives him pains.
 
I think people see more negatives in smoking than in drinking and certain drugs.  
Just a guess.

@SeraphimDawn
 
A-There is a same and beneficial limit to alcohol.
 
B-Drugs are obviously illegal that and therefore art of those is obviously depicting illegal acts (though I don’t fav the bullshit 420 images)
 
C-Smoking is something that is legal and only harmful to a persons body.

@deathsia  
I was originally going to make a snappier comment about things we’re trying to keep out of children’s mouths, but I wasn’t sure if it would be allowed by the rating and I don’t care enough about this site to do something potentially against the rules and lose my 8000+ gallery of favorited porn.

Errrr… Not that there’s anything wrong with that.  
^{Pwease don’t hurt me!}

@SeraphimDawn  
Guessing some of the people here are stoners, or drinkers.

@deathsia  
You know what baffles me?
 
Why is it that drinking and drugs are seen as acceptable here. Yet smoking is scorned?

@SeraphimDawn
 

 
for your info, this is about the smoking bit, not Fluttershy. Or at least it is to me, don’t know about these other ones here.

@deathsia  
@Background Pony  
@Roboshi  
Everyone, chill.
 
You guys really aren’t going to throw fits over an action of a fictional character. Aren’t you?

@Background Pony #0BB7
 
 
Wait,wait,wait…You think that just because he fav’d foalcon…that his creditability is any less than anyone else?
 

Alcohol and drugs, OK!
 
But tobacco? Oh no, that’s the worst thing ever!

@deathsia  
Didn’t I just say I didn’t downvote it? I don’t understand why I’m among the people you’re targetting with that statement.  
I actually agree I do think it’s well-drawn, even if I don’t like smoking, and such.

@Background Pony #0BB7
 
Sexual content can be very easily identified and kept out of the hands of the young (despite what some tumblr users think). But stuff like this can seem innocent enough, especially in other cultures, that it can work it’s way into their grasp.

@Background Pony #0BB7  
Dude, it’s Roboshi. He’ll favorite almost anything.

@Roboshi  

 
Says the person with foalcon in his favorites. :/

I knew one of these was going to rub people the wrong way.

Called it!

@deathsia  
There are no set rules for downvotes, in the same way there are no set rules fo faving (after all if there were I’d have broken them by now).
 
General rule is, people downvote the pics they don’t like. This can be because of content OR quality OR style or even the artist if they are toxic individuals.
 
Art is not created in a vacuum and you can’t expect a large mixed group of people to all judge a picture based solely on it’s artistic quality. Especially when it contains a drug that is still the subject of heated debate today.
 
I personally with not downvote this, but I will also not fave or upvote it, because personally I believe drawing a character aimed at the very young should not be depicted enjoying something we are trying to keep out of childrens mouths.
 
((Also this is exactly the sort of thing a chinese bootlegger would take and make a bag out of for fox news to make a huge fuss out of when it appears in schools))

@Background Pony #B235  
How are cigarettes edgier than, what I can only presume to be, heroin?  
There apparently really are a bunch of people on derpibooru who are just that butthurt about cigarettes.

@deathsia  
What makes you think I downvoted it? And, I’m eating pies right now. Woo!